TGFBI, CHST6, and GSN gene analysis in Mexican patients with stromal corneal dystrophies

OBJECTIVES

The purpose of our study was to describe the results of molecular screening of TGFBI, CHST6, and GSN genes in a group of Mexican patients with different stromal corneal dystrophies (CD).

MATERIAL AND METHODS

A total of 16 CD Mexican patients pertaining to nine different pedigrees were subjected to a complete ophthalmological investigation. A clinical diagnosis of lattice CD was performed in 10 patients from five pedigrees. Three patients from two pedigrees were diagnosed with granular CD type 2, two patients with unrelated probands had Finnish-type corneal amyloidosis, and one patient had macular CD. Genetic analysis included DNA isolation from blood leukocytes and polymerase chain reaction (PCR) amplification and direct nucleotide sequencing of TGFBI, CHST6, and GSN genes.

RESULTS

Seven lattice CD patients from four unrelated families had an identical p.H626R mutation in TGFBI, three patients from a single lattice CD family carried a p.R124C substitution in TGFBI, and a granular type 2 CD pedigree was demonstrated to carry a heterozygous TGFBI p.M619K substitution. A patient having Finnish-type corneal amyloidosis had a p.D187N mutation in GSN. Finally, molecular analysis of CHST6 in a patient with macular CD disclosed the presence of a homozygous p.Y110C change.

CONCLUSIONS

This study improves the knowledge of the genetic features of Mexican patients with corneal stromal dystrophies by identifying mutations in the TGFBI, CHST6, and GSN genes. Genetic screening of larger samples of patients from distinct ethnic groups would be of great importance for a better understanding of the mutational spectrum of stromal CD.

Clinical and genetic aspects of the TGFBI-associated corneal dystrophies

Corneal dystrophies are a group of inherited disorders localized to various layers of the cornea that affect corneal transparency and visual acuity. The deposition of insoluble protein materials in the form of extracellular deposits or intracellular cysts is pathognomic. Mutations in TGFBI are responsible for superficial and stromal corneal dystrophies. The gene product, transforming growth factor β induced protein (TGFBIp) accumulates as insoluble deposits in various forms. The severity, clinicopathogenic variations, age of the onset, and location of the deposits depend on the type of amino acid alterations in the protein. Until 2006, 38 different pathogenic mutants were reported for the TGFBI-associated corneal dystrophies. This number has increased to 63 mutants, reported in more than 30 countries. There is no effective treatment to prevent, halt, or reverse the deposition of TGFBIp. This review presents a complete mutation update, classification of phenotypes, comprehensive reported incidents of various mutations, and current treatment options and their shortcomings. Future research directions and possible approaches to inhibiting disease progression are discussed.

Granular corneal dystrophy type 2 is associated with morphological abnormalities of meibomian glands

AIMS

To investigate morphological changes in meibomian glands in patients with granular corneal dystrophy type 2 (GCD2) using non-invasive meibography.

METHODS

Eleven patients (3 men and 8 women) with GCD2, and sex-matched and age-matched healthy volunteers as a controls were enrolled in this study. The diagnosis of GCD2 was confirmed by transforming growth factor β-induced (TGFBI) gene analysis using direct sequencing in exon 4 of TGFBI gene. Meibography was performed in the right eye of the studied cases. Meiboscore was determined according to the morphology of meibomian gland and classified into four grades; grade 0 (no meibomian gland loss), grade 1 (loss less than one-third the total area of meibomian glands), grade 2 (area loss between one-third and two-thirds of the total area), and grade 3 (area loss greater than two-thirds of the total).

RESULTS

R124H mutation was detected in all patients with GCD2. Extinguishing or shortening of the meibomian glands was observed in patients with GCD2. The meiboscore was 3.8±1.3 in patients with GCD2 and 1.3±1.1 in the control group, showing significant difference between two groups (Mann-Whitney U-test, p=0.042).

CONCLUSIONS

In GCD2, corneal deposits, and also morphological abnormalities of meibomian glands, such as obstruction or shortening, were found. Since abnormal phospholipid deposition is noted in GCD2, these results are interesting because phospholipid is possibly secreted from the meibomian gland.

Peripheral hypertrophic subepithelial corneal degeneration: characterization, treatment and association with human leucocyte antigen genes

PURPOSE

To evaluate the efficacy of keratectomy in treating irregular astigmatism caused by peripheral hypertrophic subepithelial corneal degeneration (PHSD) and to study the possible underlying immunological risk factors.

MATERIALS AND METHODS

Patients (14 eyes) with diagnosed PHSD were treated with superficial keratectomy with or without the assistance of phototherapeutic keratectomy (VisX S4; VisX Inc., Santa Ana, CA, USA). Thirteen patients were subjected to analysis of human leucocyte antigen (HLA) genes, complement C4 gene numbers and total plasma immunoglobulin levels. Immunological risk factors between patients and a control group comprising 150 individuals were compared.

RESULTS

The mean preoperative best spectacle corrected visual acuity (BCVA) improved from 0.16 ± 0.22 (LogMAR scale range 0-0.7) to 0.06 ± 0.13 (-0.1-0.4) (p < 0.01). The mean preoperative astigmatism decreased significantly from 3.8 ± 2.1 D (range 1.2-8.2) to 2.1 ± 1.4 (range 0.6-5.0, p = 0.02) based on corneal topography. The HLA-B*44 allele and the ancestral haplotype (AH) 8.1 were found significantly more often in PHSD patients than in controls (both p = 0.03). No differences in the C4 genes were found.

CONCLUSIONS

Astigmatism secondary to PHSD can be effectively treated with keratectomy. Peeling of the fibrotic tissue reduced astigmatism and improved visual performance. We suggest that HLA-B*44 allele and AH 8.1 haplotype are immunological factors predisposing to the development of PHSD. The consequent disruption/alteration of the limbal barrier may lead to corneal peripheral fibrous formation inducing astigmatism.

A case of Korean patient with macular corneal dystrophy associated with novel mutation in the CHST6 gene

To report a novel mutation within the CHST6 gene, as well as describe light and electron microscopic features of a case of macular corneal dystrophy. A 59-year old woman with macular corneal dystrophy in both eyes who had decreased visual acuity underwent penetrating keratoplasty. Further studies including light and electron microscopy, as well as DNA analysis were performed. Light microscopy of the cornea revealed glycosaminoglycan deposits in the keratocytes and endothelial cells, as well as extracellularly within the stroma. All samples stained positively with alcian blue, colloidal iron, and periodic acid-Schiff. Electron microscopy showed keratocytes distended by membrane-bound intracytoplasmic vacuoles containing electron-dense fibrillogranular material. These vacuoles were present in the endothelial cells and between stromal lamellae. Some of the vacuoles contained dense osmophilic whorls. A novel homozygous mutation (c.613 C>T [p.Arg205Trp]) was identified within the whole coding region of CHST6. A novel CHST6 mutation was detected in a Korean macular corneal dystrophy patient.

Genetic and phenotypic investigation of a Chinese pedigree with lattice corneal dystrophy IIIB subtype

PURPOSE

To investigate phenotypes and disease-causing mutation in the transforming growth factor b-induced gene (TGFBI) in a Southern Chinese pedigree with lattice corneal dystrophy (LCD) IIIB with complicated cataract.

METHODS

A Southern Chinese pedigree with lattice corneal dystrophy IIIB with complicated cataract was recruited. Comprehensive ophthalmic investigations were performed before and after cataract surgery of phacoemulsification and intraocular lens implantation in the proband's both eyes. Peripheral blood was collected from the proband, and genomic DNA was extracted. All exons of the TGFBI gene were sequenced to screen possible mutations.

RESULTS

A bilateral LCD IIIB subtype was observed in the proband. Optical coherence tomography further revealed superreflective changes in the subepithelial and stroma layers of the cornea, with reduced central corneal thickness. Notably, bilateral cataract was found in the proband. Direct sequencing detected a recurrent heterozygous missense c.1877A > G mutation in exon 14 of the TGFBI gene, resulting in substitution of histidine with arginine (p.H626R).

CONCLUSION

The current study was the first report of the TGFBI p.H626R mutation in Southern Chinese, suggesting that it could be a mutation hotspot across populations. Moreover, the mutation was associated with LCD IIIB subtype with complicated cataract, which had not been reported before, pointing to clinical heterogeneity of the mutation.

IL1beta, IL6 and IL8 gene polymorphisms involvement in recurrent corneal erosion in patients with hereditary stromal corneal dystrophies

TGFBI gene mutations cause corneal stromal dystrophies of autosomal dominant inheritance. The most frequent complication of stromal dystrophies is recurrent corneal erosion with varying degree of accompanying inflammation. IL-1beta, IL-6 and IL-8 are main cytokines involved in corneal erosion healing. This study aimed to investigate the association between IL1B gene -511C/T, IL6 gene -174G/C and IL8 gene -781C/T polymorphisms and risk of recurrent erosion development in patients with hereditary corneal stromal dystrophies. A trend to decrease of IL1B gene -511TT genotype frequency in group with erosion (3.7%) comparing to control (6.7%) was observed. IL6 gene -174C allele carriers frequency in control group (65.9%) was significantly (P < 0.05) lower comparing to patients with erosion (80.5%). Frequency of IL8 -781TT genotype was significantly (P < 0.05) lower in the group with erosion (10.7%) comparing to patients without erosion (30.8%) and control (25%). IL6 gene -174C allele may be considered as genetic marker of corneal erosion risk in patients with hereditary stromal corneal dystrophies, whereas IL8 -781TT genotype is associated with negative recurrent erosion prognosis in such patients.

Clinical outcomes of phototherapeutic keratectomy in eyes with Thiel-Behnke corneal dystrophy

PURPOSE

To investigate the functional and morphologic midterm outcome of phototherapeutic keratectomy (PTK) for Thiel-Behnke corneal dystrophy diagnosed by gene-mutation analysis.

DESIGN

Retrospective, single-center clinical study.

METHODS

Between July 2001 and May 2010, 10 consecutive PTKs were performed in 10 eyes of 5 patients (2 male, 3 female; mean age: 55 ± 13 years) with superficially accentuated opacities caused by Thiel-Behnke corneal dystrophy and were followed up for at least 12 months (range: 12-108 months). Main outcome measures included (1) best-corrected visual acuity (BCVA), (2) uncorrected visual acuity (UCVA), (3) spherical equivalent, and (4) recurrence rate. The probability of recurrence of Thiel-Behnke corneal dystrophy after PTK was calculated using the Kaplan-Meier method for survival analysis.

RESULTS

The p.Arg555Gln mutation was found within the TGFBI gene in all 5 patients. Average logarithm of minimal angle of resolution (logMAR) BCVA change was -0.55 ± 0.26. Average logarithm UCVA change was -0.54 ± 0.31. In 5 of the 10 eyes, recurrence of central superficial opacification was clinically identified during the follow-up periods, and in 4 of those 5 eyes, the level of the recurrence was so significant that the visual acuity was reduced more than 2 lines. The maximum follow-up period of the 1 eye without significant post-PTK recurrence was 108 months.

CONCLUSIONS

PTK is a successful therapy for Thiel-Behnke corneal dystrophy, and results in midterm stable visual acuity and corneal transparency. Unlike in Reis-Bücklers corneal dystrophy cases, PTK delays the need for more invasive surgical intervention in Thiel-Behnke corneal dystrophy.

[Mutation in the UBIAD1 gene of a Chinese family with Schnyder crystal corneal dystrophy]

OBJECTIVE

To investigate the genetic feature of Schnyder corneal dystrophy identified in a four-generation Chinese family.

METHOD

Ophthalmologic examinations were performed in 3 affected members and 2 unaffected members of a family with Schnyder corneal dystrophy and controls. Genomic DNA was extracted from peripheral blood. The coding regions, 3'UTR and 5'UTR of UBIAD1 gene from all samples were screened by polymerase chain reaction (PCR) and direct DNA sequencing using the primers designed according to the sequence of UBIAD1, and comparatively analyzed with data from Genebank.

RESULT

The family has 15 members over 4 generations with similar signs and symptoms among proband and affected members. All affected members of the family demonstrated central discoid crystalline deposition with arcus lipoide. Confocal microscopy examination showed multiple depositions of crystalline materials in anterior stroma. OCT showed the high reflective material localized within the anterior stroma. A missense mutation c.305A > G in 1 exon of UBIAD1 gene resulting in a substitution of Asparagine to Serine at codon 102 (p.Asn102Ser) was found in all affected members of the family who were clinically diagnosed as Schnyder corneal dystrophy while not in the unaffected members of the family and controls.

CONCLUSION

The missense mutation c.305A > G(p.Asn102Ser) of UBIAD1 gene may cause the disease of the family. Gene screen can assist clinicians in making definitive diagnosis, presymptomatic diagnosis and prenatal diagnosis.

Establishment of a human conjunctival epithelial cell line lacking the functional TACSTD2 gene (an American Ophthalmological Society thesis)

PURPOSE

To report the establishment of a human conjunctival epithelial cell line lacking the functional tumor-associated calcium signal transducer 2 (TACSTD2) gene to be used as an in vitro model of gelatinous drop-like corneal dystrophy (GDLD), a rare disease in which the corneal epithelial barrier function is significantly compromized by the loss of function mutation of the TACSTD2 gene.

METHODS

A small piece of conjunctival tissue was obtained from a GDLD patient. The conjunctival epithelial cells were enzymatically separated and dissociated from the tissue and immortalized by the lentiviral introduction of the SV40 large T antigen and human telomerase reverse transcriptase (hTERT) genes. Population doubling, protein expression, and transepithelial resistance (TER) analyses were performed to assess the appropriateness of the established cell line as an in vitro model for GDLD.

RESULTS

The life span of the established cell line was found to be significantly elongated compared to nontransfected conjunctival epithelial cells. The SV40 large T antigen and hTERT genes were stably expressed in the established cell line. The protein expression level of the tight junction-related proteins was significantly low compared to the immortalized normal conjunctival epithelial cell line. TER of the established cell line was found to be significantly low compared to the immortalized normal conjunctival epithelial cell line.

CONCLUSIONS

Our conjunctival epithelial cell line was successfully immortalized and well mimicked several features of GDLD corneas. This cell line may be useful for the elucidation of the pathogenesis of GDLD and for the development of novel treatments for GDLD.

[Progress in the studies of molecular genetics in Bietti crystalline corneoretinal dystrophy]

CYP4V2, a relatively new member of human cytochrome P450 (P450) enzymes, is termed an "orphan" P450 because its substrate specificity and physiological roles are unknown. Mutations in the CYP4V2 gene is associated with an autosomal recessive inherited ocular disease named Bietti's crystalline dystrophy (BCD). The strong gene-disease associations provide unique opportunities for elucidating the substrate specificity of this orphan P450s and unraveling the biochemical pathways that may be impacted in patients with CYP4V2 functional deficits.

DNA nanoparticle-mediated ABCA4 delivery rescues Stargardt dystrophy in mice

Mutations in the photoreceptor-specific flippase ABCA4 are associated with Stargardt disease and many other forms of retinal degeneration that currently lack curative therapies. Gene replacement is a logical strategy for ABCA4-associated disease, particularly given the current success of traditional viral-mediated gene delivery, such as with adeno-associated viral (AAV) vectors. However, the large size of the ABCA4 cDNA (6.8 kbp) has hampered progress in the development of genetic treatments. Nonviral DNA nanoparticles (NPs) can accommodate large genes, unlike traditional viral vectors, which have capacity limitations. We utilized an optimized DNA NP technology to subretinally deliver ABCA4 to Abca4-deficient mice. We detected persistent ABCA4 transgene expression for up to 8 months after injection and found marked correction of functional and structural Stargardt phenotypes, such as improved recovery of dark adaptation and reduced lipofuscin granules. These data suggest that DNA NPs may be an excellent, clinically relevant gene delivery approach for genes too large for traditional viral vectors.

Franceschetti hereditary recurrent corneal erosion

PURPOSE

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

DESIGN

Observational case series.

METHODS

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

RESULTS

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

CONCLUSION

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

Expression, purification and characterization of fourth FAS1 domain of TGFβIp-associated corneal dystrophic mutants

Corneal dystrophies (CDs) are a group of inherited bilateral disorders affecting the corneal tissue of the eye. Most of these CDs in the stromal layer of the cornea have been associated with mutations found on the TGFBI gene that codes for a 683-amino acid transforming growth factor induced protein (TGFβIp). These mutations have been found to induce atypical aggregation and progressive accumulation of protein aggregates in the cornea that leads to loss of corneal transparency and hence blindness. At present, 65 distinct pathogenic mutations have been identified in TGFBI that are associated with different clinical phenotypes. More than 80% of these missense mutations occur in the 4th FAS (fasciclin-like) 1 domain. Current treatment includes surgical intervention, which often involves high recurrence rates. Hence, it is imperative to examine the properties of the TGFβIp and the pathogenic mutant proteins to understand the pathology of the disease mechanism and to develop potent therapeutics. Here, we report the recombinant expression, purification, characterization and the effect of four clinically significant pathogenic TGFβIp mutants - R555W, H572R, A620D, and H626R on the biophysical properties of the wild type (WT) 4th FAS1 domain of TGFβIp. While a higher proportion of the R555W, H572R and H626R mutants of the 4th FAS1 domains remained stable, the A620D mutant largely existed as inclusion bodies in native state and aggregates under physiological conditions. These mutants present a unique platform to examine protein aggregation-prone diseases wherein single amino-acid mutations present distinct pathogenic phenotypes. Though pathogenically and phenotypically diverse, these mutants do not exhibit variations in secondary structure and stability, except for the A620D mutant, when examined by CD and UV spectroscopy.

Mechanism of all-trans-retinal toxicity with implications for stargardt disease and age-related macular degeneration

Compromised clearance of all-trans-retinal (atRAL), a component of the retinoid cycle, increases the susceptibility of mouse retina to acute light-induced photoreceptor degeneration. Abca4(-/-)Rdh8(-/-) mice featuring defective atRAL clearance were used to examine the one or more underlying molecular mechanisms, because exposure to intense light causes severe photoreceptor degeneration in these animals. Here we report that bright light exposure of Abca4(-/-)Rdh8(-/-) mice increased atRAL levels in the retina that induced rapid NADPH oxidase-mediated overproduction of intracellular reactive oxygen species (ROS). Moreover, such ROS generation was inhibited by blocking phospholipase C and inositol 1,4,5-trisphosphate-induced Ca(2+) release, indicating that activation occurs upstream of NADPH oxidase-mediated ROS generation. Because multiple upstream G protein-coupled receptors can activate phospholipase C, we then tested the effects of antagonists of serotonin 2A (5-HT(2A)R) and M(3)-muscarinic (M(3)R) receptors and found they both protected Abca4(-/-)Rdh8(-/-) mouse retinas from light-induced degeneration. Thus, a cascade of signaling events appears to mediate the toxicity of atRAL in light-induced photoreceptor degeneration of Abca4(-/-)Rdh8(-/-) mice. A similar mechanism may be operative in human Stargardt disease and age-related macular degeneration.

A single-base substitution in the seed region of miR-184 causes EDICT syndrome

PURPOSE

To investigate the cause of the syndrome characterized by endothelial dystrophy, iris hypoplasia, congenital cataract, and stromal thinning (EDICT).

METHODS

Previously a multigenerational family was reported that comprised 10 individuals affected by syndromal anterior segment dysgenesis. Blood samples were re-collected from eight affected and two unaffected individuals, and genomic DNA was extracted. A total of 24 candidate genes and 4 microRNAs residing within the critical interval were sequenced bidirectionally. In silico analyses were performed to examine the effect of the causal variant on the stability of the pre-microRNA structure.

RESULTS

Bidirectional sequencing identified the single-base substitution +57C>T in miR-184. This variation segregated with the disease phenotype and was absent in the 1000 Genomes project, 1130 control chromosomes, and 28 nonhuman vertebrates.

CONCLUSIONS

The single-base-pair substitution in the seed region of miR-184 is responsible for the disease phenotype observed in EDICT syndrome.

Molecular genetic analysis of macular corneal dystrophy patients from North India

PURPOSE

To identify underlying genetic defects in the carbohydrate sulfotransferase-6 (CHST6) gene in North Indian patients with macular corneal dystrophy (MCD).

METHODS

30 clinically diagnosed MCD patients from 21 families and 50 healthy normal controls were recruited in the study. Detailed clinical evaluation in the patients was undertaken followed by histopathology and ultrastructural studies in corneal tissues. DNA from blood samples was amplified for the CHST6 coding and upstream region followed by direct sequencing and in silico analysis.

RESULTS

We identified pathogenic mutations in 17 patients from 11 families. Of these 4 were novel (p.Ser54Tyr, p.Gln58Arg, p.Leu59His and p.Leu293Phe), 2 were previously reported (Arg93His and Glu274Lys) homozygous, 1 heterozygous stop codon (p.Trp123X) and 2 compound heterozygous (p.Arg93His + p.Arg97Pro; p.Leu22Arg + p.Gln58X) mutations. A missense single-nucleotide polymorphism was also identified in 11 patients. The novel mutations were conserved as shown by in silico analysis. Thirteen patients did not show any pathogenic CHST6 changes.

CONCLUSIONS

This is the first report on molecular analysis of MCD in North Indian patients. All cases could not be explained by mutations in CHST6, suggesting that MCD may result from other changes in the regulatory elements of CHST6 or from genetic heterogeneity.

[New international classification of corneal dystrophies (CD)]

The Cornea Society founded an international committee of 17 corneal experts from the USA, Asia and Europe in 2005. The goal of this group was to develop a new international classification of corneal dystrophies (CD) based on modern clinical, histological and genetic knowledge. Both authors are members of this committee. The elaboration of the classification included the correction of many misinterpretations with regard to the different forms of CD which were published in the past literature. In spite of important results concerning the genetic locus and identification of genes and mutations, corneal dystrophies are typically classified with respect to the level of the cornea that is involved. An accurate and up-to-date template for each form of the 25 CDs was created that included the current clinical, histological and genetic information. To indicate the level of evidence supporting the existence of a given dystrophy, the CDs are divided into four different categories. The new international classification of CDs was published in English, Spanish and German as a 40 page supplement with 64 figures, mostly in color. A more detailed description of genetic mutations is included in the appendix.

The characterization of functional disturbances in Chinese patients with Bietti's crystalline dystrophy at different fundus stages

PURPOSE

The aim of this study was to characterize the functional and clinical disturbances and screen the optimal functional tests in assessing Bietti's crystalline dystrophy (BCD) patients by a cross-sectional method.

METHODS

The clinical characteristics of BCD were studied in 15 Chinese patients using fundoscopy, fundus fluorescein angiography (FFA), and autofluorescence (AF). The functional features were evaluated by full-field electroretinography (fERG), 85º and 30º perimetry, multifocal ERG (mERG), and chromatic pupillometry.

RESULTS

The 15 patients were separated into three clinical stages according to their fundus features. fERG- and mERG- showed reduced reponses in the early stages. Substages could be further defined according to the fERG results in the intermediate stages. Reduced pupillary light reflex (PLR) activities with blue-and white-light stumili existed in all patients. The most reduced PLR activities were elicited in the advanced stage of patients who had other nonresponsive functional tests.

CONCLUSIONS

This study identified the most sensitive functional methods for assessing BCD patients, and the significance of PLR in the advanced stages. In addition, the defined-substages can help us understand the disease more clearly.

Pathogenic mutations of TGFBI and CHST6 genes in Chinese patients with Avellino, lattice, and macular corneal dystrophies

OBJECTIVE

To investigate gene mutations associated with three different types of corneal dystrophies (CDs), and to establish a phenotype-genotype correlation.

METHODS

Two patients with Avellino corneal dystrophy (ACD), four patients with lattice corneal dystrophy type I (LCD I) from one family, and three patients with macular corneal dystrophy type I (MCD I) were subjected to both clinical and genetic examinations. Slit lamp examination was performed for all the subjects to assess their corneal phenotypes. Genomic DNA was extracted from peripheral blood leukocytes. The coding regions of the human transforming growth factor β-induced (TGFBI) gene and carbohydrate sulfotransferase 6 (CHST6) gene were amplified by polymerase chain reaction (PCR) and subjected to direct sequencing. DNA samples from 50 healthy volunteers were used as controls.

RESULTS

Clinical examination showed three different phenotypes of CDs. Genetic examination identified that two ACD subjects were associated with homozygous R124H mutation of TGFBI, and four LCD I subjects were all associated with R124C heterozygous mutation. One MCD I subject was associated with a novel S51X homozygous mutation in CHST6, while the other two MCD I subjects harbored a previously reported W232X homozygous mutation.

CONCLUSIONS

Our study highlights the prevalence of codon 124 mutations in the TGFBI gene among the Chinese ACD and LCD I patients. Moreover, we found a novel mutation among MCD I patients.

Novel CHST6 gene mutations in 2 unrelated cases of macular corneal dystrophy

PURPOSE

To investigate the possible mutations in the carbohydrate sulfotransferase 6 (CHST6) gene of 2 unrelated cases of macular corneal dystrophy (MCD) and to report atypical stromal deposits in one of them.

METHODS

Corneal tissues were stained with antisulfated keratan sulfate (KS), antitransforming growth factor beta 1-induced protein (TGFBIp), thioflavin-T, alcian blue, and Masson trichrome. Sequencing was performed to identify potential mutations in the CHST6 gene and the fourth and twelfth exons of the TGFBI gene.

RESULTS

Alcian blue staining revealed the presence of multiple subepithelial and intrastromal mucopolysaccharide deposits, confirming the diagnosis of MCD in both cases. Immunofluorescence staining in case 1 revealed the presence of sulfated KS only in the keratocytes and select endothelial cells, consistent with MCD type IA. Preferential expression of sulfated KS was observed in keratocytes and extracellular stromal matrix in case 2, consistent with MCD type II. Atypical subepithelial and superficial stromal deposits were observed in case 1, which stained positively with alcian blue, eosin, Masson trichrome, and thioflavin-T indicating the presence of hyaline and amyloid materials. CHST6 gene sequencing revealed 2 heterozygous mutations in case 1 (a p.Arg211Gln and a novel mutation of p.Arg177Gly) and a novel homozygous mutation of p.Pro186Arg in case 2. No mutations were found in exons 4 or 12 of the TGFBI gene in case 1.

CONCLUSIONS

Secondary hyalinosis and amyloidosis occur in a case of MCD type IA with a novel p.Arg177Gly mutation in CHST6. A novel p.Pro186Arg mutation in CHST6 is associated with MCD type II in an African American.

Clinical and basic aspects of gelatinous drop-like corneal dystrophy

Gelatinous drop-like corneal dystrophy (GDLD) was first reported in 1914 as a peculiar corneal dystrophy with an autosomal recessive inheritance mode. GDLD is rare in many countries, but relatively prevalent in Japan. The typical finding of GDLD is grayish, mulberry-like, protruding subepithelial depositions with a prominent hyperfluorescence of the cornea. Histologically, GDLD corneas are characterized by subepithelial amyloid depositions that were identified as lactoferrin by amino acid sequencing analysis. In 1998, the TACSTD2 gene was identified as a causative gene for this disease through a linkage analysis and a candidate gene approach. To date, 14 reports have demonstrated 21 mutations comprised of 9 missense, 6 nonsense, and 6 frameshift mutations from 9 ethnic back grounds. Currently, it is hypothesized that the loss of TACSTD2 gene function causes decreased epithelial barrier function, thereby facilitating tear fluid permeation into corneal tissue, the permeated lactoferrin then transforming into amyloid depositions via an unknown mechanism. For the visual rehabilitation of patients with GDLD, ophthalmologists currently employ various types of keratoplasties; however, almost all patients will experience a recurrence of the disease within a few years after such interventions. Wearing of a soft contact lens is sometimes considered as an alternative treatment for GDLD.

[Clinical observation of posterior polymorphous corneal dystrophy]

OBJECTIVE

To research the clinical features and in vivo confocal microscopic findings of posterior polymorphous corneal dystrophy (PPCD).

METHODS

It was a retrospective consecutive case study. Ten patients with PPCD, attended at Optometry Department of Henan Eye Institute from March 2007 to August 2009, were analyzed. All the subjects were examined by slit-lamp, OrbscanII, specular microscopy, HRT3/RCM confocal microscopy. Mann-Whitney U test was used to analysis the data.

RESULTS

The age of the patients ranged from 8 to 35 years. Seven eyes of the 4 patients have the vesicular lesions, five eyes of the 5 patients were band lesions and 1 patient had bilateral diffused opacities, this patient also had iridocorneal adhesions with associated papillary ectropion but without glaucoma. In total, 14 eyes of the 10 patients had PPCD. Two eyes had abnormal OrbscanII topography, it showed both anterior and posterior surface protrusion. Specular microscopy exam indicated large cells in size and reduced endothelium density. The mean size of the affected eye was 584 µm(2), the normal eye was 316 µm(2). The difference was statistically significant (U = 0.000, P = 0.002). The density of the endothelium was 1746 cells/mm(2) in affected eye and 3201 cells/mm(2) in normal eye. The difference was also statistically significant (U = 0.000, P = 0.002). In vivo confocal microscopy showed endothelial polymorphism. Occasional bright endothelial nuclei were seen. A variety of curvilinear and vesicular abnormalities were imaged including orange or finger like lesion, round or oval dark area with hyper reflectivity border. Some large lesions may lose endothelium with rough surface have a dike appearance.

CONCLUSIONS

Careful exam by slit-lamp may help to diagnose PPCD and further specular microscopy and(or) in vivo confocal microscopy exam will confirm it. Some cases may have abnormal topography, or associated with high intraocular pressure.

[Founder effect of two families with TGFBI related Thiel-Behnke corneal dystrophy]

OBJECTIVE

To investigate the transforming growth factor beta induced (TGFBI; BIGH3) gene mutation and founder effect of two large Chinese families clinically diagnosed as Thiel-Behnke corneal dystrophy.

METHODS

Fifteen members including 13 affected and 2 healthy in family A, 14 members including 6 affected and 8 healthy in family B, as well as 20 other unrelated healthy individuals were tested for TGFBI gene mutation. Haplotype analysis and clinical examination were also carried out in the two families.

RESULTS

In exon 12 of the TGFBI gene, 1664G to A change was detected in all the patients, which leads to an amino acid replacement of arginine with glutamine (p.Arg555Gln). Members of the two families share some similar haplotypes.

CONCLUSION

Genetic analysis is helpful in the diagnosis of corneal dystrophy. The two families may come from a same ancestor.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Mutation analysis of CHST6 gene in Chinese patients with macular corneal dystrophy

PURPOSE

To examine the carbohydrate sulfotransferase 6 (CHST6) gene in Chinese patients with macular corneal dystrophy (MCD).

METHODS

Nineteen unrelated Chinese families with MCD, including 24 patients and 3 unaffected relatives, were examined. Genomic DNA was extracted from peripheral blood leukocytes. The coding region of the CHST6 gene was amplified by the polymerase chain reaction, and the DNA fragments were directly sequenced. Fifty unrelated normal Chinese volunteers served as the controls.

RESULTS

Eighteen different mutations in the CHST6 gene (including 15 novel mutations) were identified, of which 12 were missense mutations, 5 were nonsense mutations, and 1 was a frameshift mutation. Six families had homozygous mutation, and 13 families had compound heterozygous mutation. None of these mutations were detected in the normal controls.

CONCLUSIONS

CHST6 mutations may be responsible for the pathogenesis of MCD in Chinese patients. The Q298X mutation detected in 5 of 19 families (6 of 38 alleles, 15.8%) may be the founder mutation in Chinese patients. However, our findings also indicate a high level of allelic heterogeneity of the CHST6 gene in Chinese patients and in other ethnic groups.

Crystal deposits on the lens capsules in Bietti crystalline corneoretinal dystrophy associated with a mutation in the CYP4V2 gene

PURPOSE

We report a patient (Case 1) with Bietti crystalline corneoretinal dystrophy (BCD) associated with previously unknown findings of crystal-like deposits on the anterior and posterior lens capsules. This patient is one of four (Cases 1-4) in whom we have found BCD associated with the same mutation in the CYP4V2 gene.

METHODS

We present a case report with molecular diagnosis. A 45-year-old man (Case 1) was referred to our clinic with complaints of gradual progression of visual disturbances and night blindness. His visual acuity was limited to hand movement bilaterally. Slit-lamp biomicroscopy disclosed glistening, crystal-like deposits on the anterior and posterior lens capsules, as well as on the corneal stroma near the corneoscleral limbus. No such deposit was found in the lens stroma. Fundus examination disclosed profound chorioretinal atrophy with scarce crystal deposits. Full-field electroretinography showed extinguished responses of isolated rods, isolated cones, and mixed rods and cones.

RESULTS

Molecular genetic analysis revealed that the subject had a homozygous mutation in the CYP4V2 gene (IVS6-8delTCATACAGGTCATCGCG/insGC), which is most commonly found in Japanese patients with BCD. Three other cases (Cases 2-4) of BCD associated with the same mutation did not show such crystal-like deposits on the lens surface.

CONCLUSIONS

Although their exact origin remains unknown, crystal-like deposits may appear on the lens capsule of patients with BCD associated with a mutation in the CYP4V2 gene.

UBIAD1 mutation alters a mitochondrial prenyltransferase to cause Schnyder corneal dystrophy

BACKGROUND

Mutations in a novel gene, UBIAD1, were recently found to cause the autosomal dominant eye disease Schnyder corneal dystrophy (SCD). SCD is characterized by an abnormal deposition of cholesterol and phospholipids in the cornea resulting in progressive corneal opacification and visual loss. We characterized lesions in the UBIAD1 gene in new SCD families and examined protein homology, localization, and structure.

METHODOLOGY/PRINCIPAL FINDINGS

We characterized five novel mutations in the UBIAD1 gene in ten SCD families, including a first SCD family of Native American ethnicity. Examination of protein homology revealed that SCD altered amino acids which were highly conserved across species. Cell lines were established from patients including keratocytes obtained after corneal transplant surgery and lymphoblastoid cell lines from Epstein-Barr virus immortalized peripheral blood mononuclear cells. These were used to determine the subcellular localization of mutant and wild type protein, and to examine cholesterol metabolite ratios. Immunohistochemistry using antibodies specific for UBIAD1 protein in keratocytes revealed that both wild type and N102S protein were localized sub-cellularly to mitochondria. Analysis of cholesterol metabolites in patient cell line extracts showed no significant alteration in the presence of mutant protein indicating a potentially novel function of the UBIAD1 protein in cholesterol biochemistry. Molecular modeling was used to develop a model of human UBIAD1 protein in a membrane and revealed potentially critical roles for amino acids mutated in SCD. Potential primary and secondary substrate binding sites were identified and docking simulations indicated likely substrates including prenyl and phenolic molecules.

CONCLUSIONS/SIGNIFICANCE

Accumulating evidence from the SCD familial mutation spectrum, protein homology across species, and molecular modeling suggest that protein function is likely down-regulated by SCD mutations. Mitochondrial UBIAD1 protein appears to have a highly conserved function that, at least in humans, is involved in cholesterol metabolism in a novel manner.

[Novel CHST6 compound heterozygous mutations cause macular corneal dystrophy in a Chinese family]

OBJECTIVE

The aim of this study was to identify mutations of CHST6 gene in a Chinese family with macular corneal dystrophy (MCD) and to investigate the histopathological changes of MCD.

METHODS

Corneal button of the proband was obtained from penetrating keratoplasty for the treatment of severe corneal dystrophy. The sections and ultrathin sections of this specimen were examined under light microscope and transmission electron microscope (TEM). Genomic DNA was extracted from leukocytes in peripheral blood from the family members. The coding region of CHST6 was amplified by polymerase chain reaction (PCR). The PCR products were analyzed by direct sequencing and restriction enzyme digestion.

RESULTS

Histochemical study revealed positive results of colloidal iron stain. TEM revealed enlargement of smooth endoplasmic reticulum and the presence of intracytoplasmic vacuoles. Two mutations, Q298X Y358H, were identified in exon 3 of CHST6. Three patients were compound heterozygotes of these two mutations. The C892T transversion occurred at codon 298 turned the codon of glutamine to a stop codon; the T1072C transversion occurred at codon 358 caused a missense mutation, tyrosine to histidine. All six unaffected family members were heterozygotes. These two mutations were not detected in any of the 100 control subjects.

CONCLUSIONS

The novel compound heterozygous mutation results in loss of CHST6 function and causes the occurrence of MCD. This is the first report of this gene mutation.

Molecular genetic study of Egyptian patients with macular corneal dystrophy

AIM

To identify the underlying genetic defect in Egyptian patients with macular corneal dystrophy (MCD).

METHODS

A clinical and molecular genetic study was performed on 11 patients from six families with MCD. Clinical diagnosis was confirmed by slit-lamp biomicroscopy and histopathological examination of corneal buttons following keratoplasty. The coding region of the carbohydrate sulfotransferase (CHST6) gene was amplified by polymerase chain reaction (PCR) in all affected subjects. This was followed by direct sequencing and restriction digest analyses. Enzyme-linked immunosorbent assay of antigenic keratan sulfate (KS) in patients' serum was also performed.

RESULTS

Six homozygous mutations, of which three are novel, were identified within the coding region of CHST6 in six unrelated MCD families. The barely detectable level of antigenic KS in the serum of the affected individuals indicated that they all have MCD type I, including the subtype IA.

CONCLUSIONS

This is the first report of a molecular genetic analysis of MCD in the Egyptian population. These data indicate the extensive allelic heterogeneity within CHST6 and further support its essential role in maintaining corneal transparency.

Missense mutations in TCF8 cause late-onset Fuchs corneal dystrophy and interact with FCD4 on chromosome 9p

Fuchs corneal dystrophy (FCD) is a degenerative genetic disorder of the corneal endothelium that represents one of the most common causes of corneal transplantation in the United States. Despite its high prevalence (4% over the age of 40), the underlying genetic basis of FCD is largely unknown. Here we report missense mutations in TCF8, a transcription factor whose haploinsufficiency causes posterior polymorphous corneal dystrophy (PPCD), in a cohort of late-onset FCD patients. In contrast to PPCD-causing mutations, all of which are null, FCD-associated mutations encode rare missense changes suggested to cause loss of function by an in vivo complementation assay. Importantly, segregation of a recurring p.Q840P mutation in a large, multigenerational FCD pedigree showed this allele to be sufficient but not necessary for pathogenesis. Execution of a genome-wide scan conditioned for the presence of the 840P allele identified an additional late-onset FCD locus on chromosome 9p, whereas haplotype analysis indicated that the presence of the TCF8 allele and the disease haplotype on 9p leads to a severe FCD manifestation with poor prognosis. Our data suggest that PPCD and FCD are allelic variants of the same disease continuum and that genetic interaction between genes that cause corneal dystrophies can modulate the expressivity of the phenotype.

[Hereditary gelsolin amyloidosis--40 years of Meretoja disease]

Hereditary gelsolin amyloidosis is an autosomally dominantly inherited systemic disease, first described in 1969 by the Finnish ophthalmologist Jouko Meretoja. The estimated number of disease carriers in Finland is almost 1 000, and the disease has subsequently been found in many other countries as well. It's typical initial manifestation is lattice corneal dystrophy, detected at biomicroscopic examination of the eye by the age of 25 to 30 years, followed by slowly progressing cranial neuropathy with bilateral facial palsy, polyneuropathy and generalized cutis laxa. Meretoja's disease is caused by mutations of the gelsolin gene, leading to the production and aberrant processing of variant gelsolin and deposition of its fragments in various tissues in the form of amyloid fibrils.

R555W mutation of TGFbetaI related to granular corneal dystrophy in Chinese patients

BACKGROUND

Mutations in the transforming growth factor beta I (TGFBI) gene cause several types of autosomal-dominant corneal dystrophies. We investigated the role of this gene in a Chinese family affected by granular corneal dystrophy (GCD).

METHODS

Family history and phenotypic data were recorded. The diagnosis of GCD was made on the basis of clinical evaluation. The genomic DNA was extracted from peripheral blood leukocytes. All the exons and flanking intron-exon boundary sequences of TGFbetaI were amplified by polymerase chain reaction (PCR) and screened for mutation by direct DNA sequencing.

RESULTS

A heterozygous C to T transition at nucleotide c.1663 (CGG to TGG R555W) of TGFbetaI gene was present in two affected members but was absent in the rest of the family members.

CONCLUSION

A recurrent pathogenic R555W of TGFbetaI gene mutation is identified, which appears to be the predominant mutations causing GCD in different populations.

Corneal dystrophy-associated R124H mutation disrupts TGFBI interaction with Periostin and causes mislocalization to the lysosome

The 5q31-linked corneal dystrophies are heterogeneous autosomal-dominant eye disorders pathologically characterized by the progressive accumulation of aggregated proteinaceous deposits in the cornea, which manifests clinically as severe vision impairment. The 5q31-linked corneal dystrophies are commonly caused by mutations in the TGFBI (transforming growth factor-beta-induced) gene. However, despite the identification of the culprit gene, the cellular roles of TGFBI and the molecular mechanisms underlying the pathogenesis of corneal dystrophy remain poorly understood. Here we report the identification of periostin, a molecule that is highly related to TGFBI, as a specific TGFBI-binding partner. The association of TGFBI and periostin is mediated by the amino-terminal cysteine-rich EMI domains of TGFBI and periostin. Our results indicate that the endogenous TGFBI and periostin colocalize within the trans-Golgi network and associate prior to secretion. The corneal dystrophy-associated R124H mutation in TGFBI severely impairs interaction with periostin in vivo. In addition, the R124H mutation causes aberrant redistribution of the mutant TGFBI into lysosomes. We also find that the periostin-TGFBI interaction is disrupted in corneal fibroblasts cultured from granular corneal dystrophy type II patients and that periostin accumulates in TGFBI-positive corneal deposits in granular corneal dystrophy type II (also known as Avellino corneal dystrophy). Together, our findings suggest that TGFBI and periostin may play cooperative cellular roles and that periostin may be involved in the pathogenesis of 5q31-linked corneal dystrophies.

[Analysis of TGFBI gene mutation in a Chinese family with atypical Reis-Buckler corneal dystrophy]

OBJECTIVE

To identify the TGFBI gene mutation and the relationship between genotype and phenotype of a Chinese family with atypical Reis-Buckler corneal dystrophy (RBCD).

METHODS

Four patients, two non-carrier relatives of the family were enrolled in the present study. In addition to ophthalmologic examinations, PCR amplification and DNA sequencing of exons 4, 11, 12, and 14 of the TGFBI gene were carried out. Exon 14 was also sequenced in 100 healthy controls.

RESULTS

A G to A transition at codon 623 in all affected members was identified. This mutation resulted in a substitution of glycine (GGC) to aspartic acid (GAC) at the protein level.None of the healthy family members, or any of the 100 control subjects carried this mutation.

CONCLUSION

The G623D mutation of the TGFBI gene caused an atypical Reis-Buckler corneal dystrophy in this family. This mutation is reported in Chinese for the first time.

Application of homozygosity haplotype analysis to genetic mapping with high-density SNP genotype data

Background

In families segregating a monogenic genetic disorder with a single disease gene introduction, patients share a mutation-carrying chromosomal interval with identity-by-descent (IBD). Such a shared chromosomal interval or haplotype, surrounding the actual pathogenic mutation, is typically detected and defined by multipoint linkage and phased haplotype analysis using microsatellite or SNP genotype data. High-density SNP genotype data presents a computational challenge for conventional genetic analyses. A novel non-parametric method termed Homozygosity Haplotype (HH) was recently proposed for the genome-wide search of the autosomal segments shared among patients using high density SNP genotype data.

Methodology/Principal Findings

The applicability and the effectiveness of HH in identifying the potential linkage of disease causative gene with high-density SNP genotype data were studied with a series of monogenic disorders ascertained in eastern Canadian populations. The HH approach was validated using the genotypes of patients from a family affected with a rare autosomal dominant disease Schnyder crystalline corneal dystrophy. HH accurately detected the ∼1 Mb genomic interval encompassing the causative gene UBIAD1 using the genotypes of only four affected subjects. The successful application of HH to identify the potential linkage for a family with pericentral retinal disorder indicates that HH can be applied to perform family-based association analysis by treating affected and unaffected family members as cases and controls respectively. A new strategy for the genome-wide screening of known causative genes or loci with HH was proposed, as shown the applications to a myoclonus dystonia and a renal failure cohort.

Conclusions/Significance

Our study of the HH approach demonstrates that HH is very efficient and effective in identifying potential disease linked region. HH has the potential to be used as an efficient alternative approach to sequencing or microsatellite-based fine mapping for screening the known causative genes in genetic disease study.

Macular corneal dystrophy in a Chinese family related with novel mutations of CHST6

PURPOSE

To identify mutations in the carbohydrate sulfotransferase gene (CHST6) for a Chinese family with macular corneal dystrophy (MCD) and to investigate the histopathological changes in the affected cornea.

METHODS

A corneal button of the proband was obtained by penetrating keratoplasty. The half button and ultrathin sections from the other half button were examined with special stains under a light microscope (LM) and an electron microscope (EM) separately. Genomic DNA was extracted from peripheral blood of 11 family members, and the coding region of CHST6 was amplified by the polymerase chain reaction (PCR) method. The PCR products were analyzed by direct sequencing and restriction enzyme digestion.

RESULTS

The positive reaction to colloidal iron stain (extracellular blue accumulations in the stroma) was detected under light microscopy. Transmission electron microscopy revealed the enlargement of smooth endoplasmic reticulum and the presence of intracytoplasmic vacuoles. The compound heterozygous mutations, c.892C>T and c.1072T>C, were identified in exon 3 of CHST6 in three patients. The two transversions resulted in the substitution of a stop codon for glutamine at codon 298 (p.Q298X) and a missense mutation at codon 358, tyrosine to histidine (p.Y358H). The six unaffected family individuals carried alternative heterozygous mutations. These two mutations were not detected in any of the 100 control subjects.

CONCLUSIONS

Those novel compound heterozygous mutations were thought to contribute to the loss of CHST6 function, which induced the abnormal metabolism of keratan sulfate (KS) that deposited in the corneal stroma. It could be proved by the observation of a positive stain reaction and the enlarged collagen fibers as well as hyperplastic fibroblasts under microscopes.

Corneal dystrophies

The term corneal dystrophy embraces a heterogenous group of bilateral genetically determined non-inflammatory corneal diseases that are restricted to the cornea. The designation is imprecise but remains in vogue because of its clinical value. Clinically, the corneal dystrophies can be divided into three groups based on the sole or predominant anatomical location of the abnormalities. Some affect primarily the corneal epithelium and its basement membrane or Bowman layer and the superficial corneal stroma (anterior corneal dystrophies), the corneal stroma (stromal corneal dystrophies), or Descemet membrane and the corneal endothelium (posterior corneal dystrophies). Most corneal dystrophies have no systemic manifestations and present with variable shaped corneal opacities in a clear or cloudy cornea and they affect visual acuity to different degrees. Corneal dystrophies may have a simple autosomal dominant, autosomal recessive or X-linked recessive Mendelian mode of inheritance. Different corneal dystrophies are caused by mutations in the CHST6, KRT3, KRT12, PIP5K3, SLC4A11, TACSTD2, TGFBI, and UBIAD1 genes. Knowledge about the responsible genetic mutations responsible for these disorders has led to a better understanding of their basic defect and to molecular tests for their precise diagnosis. Genes for other corneal dystrophies have been mapped to specific chromosomal loci, but have not yet been identified. As clinical manifestations widely vary with the different entities, corneal dystrophies should be suspected when corneal transparency is lost or corneal opacities occur spontaneously, particularly in both corneas, and especially in the presence of a positive family history or in the offspring of consanguineous parents. Main differential diagnoses include various causes of monoclonal gammopathy, lecithin-cholesterol-acyltransferase deficiency, Fabry disease, cystinosis, tyrosine transaminase deficiency, systemic lysosomal storage diseases (mucopolysaccharidoses, lipidoses, mucolipidoses), and several skin diseases (X-linked ichthyosis, keratosis follicularis spinolosa decalvans). The management of the corneal dystrophies varies with the specific disease. Some are treated medically or with methods that excise or ablate the abnormal corneal tissue, such as deep lamellar endothelial keratoplasty (DLEK) and phototherapeutic keratectomy (PTK). Other less debilitating or asymptomatic dystrophies do not warrant treatment. The prognosis varies from minimal effect on the vision to corneal blindness, with marked phenotypic variability.