Early and late clinical landmarks of corneal dystrophies

Corneal dystrophies (CDs) represent a heterogenous group of genetic diseases (Lisch and Weiss, 2019). The International Committee of Classification of Corneal Dystrophies (IC3D) distinguishes between 22 distinct forms of corneal dystrophy (CD) which are predominantly autosomal dominant, although autosomal recessive and X-chromosomal dominant and recessive patterns do exist. A detailed corneal examination of as many affected family members as possible can show the phenotypic differences of the various generations. There are few publications which describe the different CDs with regard to the early and late phenotypes. According to early and late phenotype, three types of CD are generally classified: (1) Thirteen CDs with early and late clinical landmarks. However, it must be pointed out that the different penetrances of the gene often leads to quantitative differences in the corneal phenotype in peers in distinct generations of the same family. (2) Seven CDs with late onset and very little progression of the corneal changes. (3) Two CDs with congenital haze which can be interpreted as the final phenotype of this dystrophy. This applies to autosomal dominant and recessive inheritance.

The Genetics and Pathophysiology of IC3D Category 1 Corneal Dystrophies: A Review

Corneal dystrophies are a group of inherited disorders affecting the cornea, many of which lead to visual impairment. The International Committee for Classification of Corneal Dystrophies has established criteria to clarify the status of the various corneal dystrophies, which include the knowledge of the underlying genetics. In this review, we discuss the International Committee for Classification of Corneal Dystrophies category 1 (second edition) corneal dystrophies, for which a clear genetic link has been established. We highlight the various mechanisms underlying corneal dystrophy pathology, including structural disorganization, instability or maladhesion, aberrant protein stability and deposition, abnormal cellular proliferation or apoptosis, and dysfunction of normal enzymatic processes. Understanding these genetic mechanisms is essential for designing targets for therapeutic intervention, especially in the age of gene therapy and gene editing.

[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.

What's in a name: keratoconus, pellucid marginal degeneration, and related thinning disorders

PURPOSE

To discuss the implications of the current nomenclature and use of current diagnostic modalities on the classification and treatment of pellucid marginal degeneration and keratoconus.

DESIGN

Perspective analysis of the literature.

METHODS

Analysis of published reports on the various treatment methods for pellucid marginal degeneration and keratoconus, and the technologies used in these studies to support the diagnosis and classification of these ectatic disorders.

RESULTS

Many studies exploring the different treatment modalities for pellucid marginal degeneration and keratoconus rely mainly on anterior curvature maps to establish the diagnosis of these ectatic disorders, and either do not utilize or disregard information provided by pachymetric maps and posterior elevation maps. In addition, the interchangeability of the nomenclature used to describe these disorders in the literature makes it even more difficult for the clinician to determine the applicability of the results to their patient population.

CONCLUSIONS

We propose that future studies minimally include anterior and posterior elevation maps, anterior curvature topography, and full pachymetric maps. This will allow practitioners a better understanding of the study population, and allow them to ascertain when and in whom the treatment modality being explored may be applicable.

IC3D classification of corneal dystrophies

The International Committee for Classification of Corneal Dystrophies (IC3D) has provided an update of our knowledge on corneal dystrophies. This chapter gives the summary of clinical findings, onset, course, genetics, nosology, light and electron microscopy as well as immunohistochemistry for 25 different entities included as corneal dystrophies in this survey. A category number from 1 through 4 is assigned, reflecting the level of evidence supporting the existence of a given dystrophy.

Dystrophia Helsinglandica: a new type of hereditary corneal recurrent erosions with late subepithelial fibrosis

PURPOSE

To describe the phenotype of an autosomal-dominant corneal dystrophy with an early onset of recurrent corneal erosions and development of subepithelial fibrosis in the cornea, and also to exclude genetic linkage to known corneal dystrophies with autosomal-dominant inheritance and clinical resemblance.

METHODS

We describe the medical history and clinical findings in individuals from a seven-generation family with recurrent corneal erosions. A total of 43 individuals were evaluated by ophthalmological examination. Genomic DNA was prepared from peripheral blood and polymorphic microsatellite markers were analysed to study haplotypes surrounding genes causing corneal dystrophies with similar phenotypes.

RESULTS

Erosive symptoms usually lasted for between 1 and 10 days. By the age of 7 almost all of the affected individuals suffered from recurrent corneal erosions. The attacks generally declined in frequency and intensity from the late 20s, but all examined individuals had developed subepithelial fibrosis by the age of 37. The fibrosis generally started in the mid periphery and was followed in some family members by central fibrosis and the development of gelatinous superficial elevations. Only a marginal reduction of visual acuity was seen in a few individuals. The affected individuals did not share haplotypes for genetic microsatellite markers surrounding genes that are known to cause autosomal-dominant corneal dystrophies.

CONCLUSION

We describe a new type of autosomal-dominant corneal disorder with recurrent corneal erosions and subepithelial fibrosis not significantly affecting visual acuity.

The IC3D classification of the corneal dystrophies

BACKGROUND

The recent availability of genetic analyses has demonstrated the shortcomings of the current phenotypic method of corneal dystrophy classification. Abnormalities in different genes can cause a single phenotype, whereas different defects in a single gene can cause different phenotypes. Some disorders termed corneal dystrophies do not appear to have a genetic basis.

PURPOSE

The purpose of this study was to develop a new classification system for corneal dystrophies, integrating up-to-date information on phenotypic description, pathologic examination, and genetic analysis.

METHODS

The International Committee for Classification of Corneal Dystrophies (IC3D) was created to devise a current and accurate nomenclature.

RESULTS

This anatomic classification continues to organize dystrophies according to the level chiefly affected. Each dystrophy has a template summarizing genetic, clinical, and pathologic information. A category number from 1 through 4 is assigned, reflecting the level of evidence supporting the existence of a given dystrophy. The most defined dystrophies belong to category 1 (a well-defined corneal dystrophy in which a gene has been mapped and identified and specific mutations are known) and the least defined belong to category 4 (a suspected dystrophy where the clinical and genetic evidence is not yet convincing). The nomenclature may be updated over time as new information regarding the dystrophies becomes available.

CONCLUSIONS

The IC3D Classification of Corneal Dystrophies is a new classification system that incorporates many aspects of the traditional definitions of corneal dystrophies with new genetic, clinical, and pathologic information. Standardized templates provide key information that includes a level of evidence for there being a corneal dystrophy. The system is user-friendly and upgradeable and can be retrieved on the website www.corneasociety.org/ic3d.

TGFBI (BIGH3) gene mutations in Hungary--report of the novel F547S mutation associated with polymorphic corneal amyloidosis

PURPOSE

To identify mutations in the Transforming Growth Factor Beta Induced (TGFBI) gene in Hungarian patients with corneal dystrophy and to characterize histological features of their corneal buttons excised during penetrating keratoplasty.

METHODS

Exons of TGFBI were sequenced in 38 members of 15 unrelated families with corneal dystrophy and exon 12 was also sequenced in 100 healthy controls from the same population. Immunohistological analysis of available corneal buttons excised during penetrating keratoplasty was also performed.

RESULTS

Molecular genetic analysis revealed a heterozygous R124C mutation in 18 patients with lattice type I dystrophy. A R555W heterozygous mutation was detected in five patients with granular Groenouw type I corneal dystrophy and a R555Q heterozygous mutation was found in four patients clinically diagnosed with Reis-Bücklers (one patient) and Thiel-Behnke (three patients) dystrophy. Three patients with "atypical granular" dystrophy later diagnosed as Avellino dystrophy were heterozygous for the R124H mutation. A novel heterozygous mutation (T1640C) causing a F547S amino acid exchange was detected in a patient with polymorphic corneal amyloidosis. Immunohistochemistry showed the presence of BIGH3 protein deposits in all examined corneal buttons. Electron microscopy confirmed the presence of amyloid fibrils in the case of the novel mutation.

CONCLUSIONS

Our results indicate that molecular genetic analysis is required to confirm the diagnosis of corneal dystrophies. We report the first cases of Avellino dystrophy from Central-Eastern Europe. We conclude that the novel F547S mutation causes polymorphic corneal amyloidosis since no other mutations were detected in the TGFBI gene of this patient and the novel mutation could not be found in healthy controls.

[The different opacity patterns of Lisch corneal dystrophy]

BACKGROUND

Lisch corneal dystrophy is an epithelial corneal dystrophy where diffuse gray corneal opacifications are seen in direct illumination that appear in different patterns. Examination in retroillumination shows that these gray changes do consist of multiple densely crowded clear microcysts according to the opacity units. We wanted to investigate if one single case of Lisch corneal dystrophy can be differentiated easily from the other epithelial corneal dystrophies by exact analysis of the opacity units.

PATIENTS AND METHODS

We examined three non-related patients with Lisch corneal dystrophy at the slit-lamp. The epithelial corneal opacities were documented photographically with direct slit-lamp illumination and retroillumination.

RESULTS

All three patients showed the characteristic intraepithelial densely crowded clear microcysts in retroillumination. Diffuse gray radial opacities were noted in both corneas of a 15-year-old female patient. A club-shaped opacity was noted in one cornea of a 35-year-old female patient and a feathery gray opacity pattern was found in one cornea of a 49-year-old male patient. All three patients showed the characteristic densely crowded clear microcysts of Lisch corneal dystrophy in retroillumination.

CONCLUSION

Taking the previous literature into account, five different opacity patterns can be summarised: radial, band, flame/feathery, whorled and club-shaped gray epithelial corneal opacities. A single case of Lisch corneal dystrophy can be differentiated from other epithelial corneal dystrophies by means of an exact analysis of the opacity pattern and units by slit-lamp examination.

[Molecular genetic and histopathological examinations for genotype-phenotype analysis in patients with TGFBI-linked corneal dystrophy]

PURPOSE

Different missense mutations in the TGFBI gene cause granular (Groenouw CDGG1, Avellino CDA, Reis-Bücklers CDB1) and lattice (Type I; Biber-Haab-Dimmer; CDL1) corneal dystrophies and, in some reports, corneal dystrophy Thiel-Behnke (CDB2). We report on the mutation spectrum and the genotype-phenotype correlations on the basis of clinical and histopathological examinations of 13 German families with TGFBI-linked corneal dystrophies.

METHODS

In 31 patients with different corneal dystrophies, DNA was extracted from leukocytes of the peripheral blood and mutation analysis was performed by direct sequencing of the TGFBI gene. Clinical and histopathological findings were compared with the molecular genetic findings for genotype-phenotype correlations.

RESULTS

In 6 patients (2 families/one single person) with clinical and histopathological CDL1 we found a Missense mutation Arg124Cys and in 7 patients (3 families/one single person) with clinical and histopathological CDA we found a Missense mutation Arg124His in the exon 4 of the TGFBI gene. In 12 patients (4 families/2 single persons) with clinical and histopathological CDGG1 we found a Missense mutation Arg555Trypt in the codon 12 of the TGFBI gene. In all five patients (1 family/4 single persons) with clinical and histopathological CDB2 we could not find any mutation in the TGFBI gene. In one patient with exceptional clinical and histopathological findings we found a Missense mutation Ala546Asp, which was reported before only twice in connection with polymorphous corneal amyloidosis.

CONCLUSIONS

In comparison of our clinical and histopathological findings and the molecular genetic results we found a strong genotype-phenotype correlation in patients with TGFBI-linked corneal dystrophies. Rare mutations can lead to exceptional clinical and histopathological findings which cannot be classified into the different groups of corneal dystrophies. In our patients with CDB2 we could not find any molecular genetic correlation to the TGFBI gene.

TGFBI gene mutations in corneal dystrophies

The lattice corneal dystrophies (LCD) and granular corneal dystrophies (GCD) are autosomal dominant disorders of the corneal stroma. They are bilateral, progressive conditions characterized by the formation of opacities arising due to the deposition of insoluble material in the corneal stroma leading to visual impairment. The LCDs and GCDs are distinguished from each other and are divided into subtypes on the basis of the clinical appearance of the opacities, clinical features of the disease, and on histopathological staining properties of the deposits. The GCDs and most types of LCD arise from mutations in the transforming growth factor beta-induced (TGFBI) gene on chromosome 5q31. Over 30 mutations causing LCD and GCD have been identified so far in the TGFBI. There are two mutation hotspots corresponding to arginine residues at positions 124 and 555 of the transforming growth factor beta induced protein (TGFBIp) and they are the most frequent sites of mutation in various populations. Mutations at either of these two hotspots result in specific types of LCD or GCD. The majority of identified mutations involve residues in the fourth fasciclin-like domain of TGFBIp.

Different mutations in carbohydrate sulfotransferase 6 (CHST6) gene cause macular corneal dystrophy types I and II in a single sibship

PURPOSE

The aim of this study was to examine the carbohydrate sulfotransferase 6 (CHST6) gene for mutations in a sibship with both macular corneal dystrophy (MCD) types I and II.

DESIGN

Clinically relevant laboratory investigation.

METHODS

The coding region of the CHST6 gene was examined for mutations.

RESULTS

In one sibling, MCD type I was due to a homozygous C1110T (Arg140end) mutation in CHST6. Two MCD type II individuals exhibited three heterozygous nucleotide changes: C1110T, G1360A (Gly223Asp), and G1685T (Gln331His). Analysis of the upstream region was performed on one individual with MCD type II, and no upstream deletion or substitution was found.

CONCLUSIONS

These findings fit the haplotype analysis that we reported previously and indicate that the predicted protein that is encoded by CHST6 is more severely affected in the individual with MCD type I than in the siblings with MCD type II.

[Case of late onset and isolated lattice corneal dystrophy with Asn544Ser (N544S) mutation of transforming growth factor beta-induced (TGFBI, BIGH3) gene]

PURPOSE

To report a case of lattice corneal dystrophy (LCD) with Asn544Ser (N544S) mutation of the transforming growth factor beta-induced (TGFBI) gene.

CASE

A 68-year-old male patient with late-onset, sporadic LCD without corneal erosion. Amyloid deposits showing dot and lattice lines were seen in the mid to deep stroma. After obtaining appropriate informed consent, genomic DNA was amplified by polymerase chain reaction (PCR) and directly sequenced.

RESULTS

A heterozygous single base pair transition (AAT --> AGT), resulting in substitution of serine for asparagine at codon 544 of the TGFBI gene, was detected.

CONCLUSION

The case was classified as atypical type IV because of the late onset, lack of corneal erosion, and amyloid deposits in the mid to deep stroma.

A spectrum of clinical manifestations of gelatinous drop-like corneal dystrophy in japan

PURPOSE

Typical manifestations of gelatinous drop-like corneal dystrophy (GDLD) have been documented in past studies. In practice, however, we see few typical cases and encounter many with atypical clinical manifestations. Moreover, there have been no detailed reports about the various clinical presentations. The purpose of this study is to describe a clinical subclassification for GDLD.

DESIGN

Observational case series.

METHODS

A retrospective, observational case series study was conducted at a single institution, Osaka University Hospital. Examined were 18 eyes of ten patients with GDLD with no prior surgery. All were found to have M1S1 mutations. Using slit-lamp examinations we performed a phenotypic classification.

RESULTS

We classified GDLD patients into four groups. They included band keratopathy type (seven eyes of four patients), stromal opacity type (five eyes of three patients), kumquat-like type (four eyes of two patients), and typical mulberry type (two eyes of two patients).

CONCLUSIONS

Gelatinous drop-like corneal dystrophy is thought to be the result of mutations in M1S1; however, it has various clinical manifestations. To our knowledge, this study is the first to report the range of clinical phenotypes of GDLD in a Japanese population. As most clinicians have no criteria for diagnosing GDLD, many cases are likely to be overlooked or be mistaken for other conditions. We believe that our present classification will be useful for the diagnosis of GDLD.

Heredit�re Netzhaut-Aderhaut-Dystrophien

A generally accepted classification for inherited retinochoroidal dystrophies does not exist. The names given to certain disorders are either based on ophthalmoscopic findings, or on histologic, electrophysiologic and genetic findings. Future research on the molecular genetic background will result in better definition of clinical entities. The purpose of this project is to outline a practical approach to inherited retinochoroidal dystrophies. For this reason, disorders with similar clinical symptoms are grouped together. Generalized retinochoroidal dystrophies affecting all retinal areas can be distinguished from regional dystrophies. Generalized dystrophies can be subdivided into those with peripheral onset, usually associated with initial rod function loss (night blindness, peripheral field loss: e.g. retinitis pigmentosa, choroideremia) and those with central onset associated with cone function loss (visual acuity loss, central scotoma, color vision deficits: e.g. cone or cone-rod dystrophies). Regionally limited dystrophies include the multitude of macular dystrophies and the autosomal dominant vitreoretinochoroidopathy, which remains limited to the periphery. It is important for a differential diagnosis to exclude involvement of other organ systems in syndromic disorders. Stationary inherited retinal dysfunction (e.g. monochromatism, congenital stationary night blindness) and other inherited or acquired diseases have to be excluded as well. Guidelines for differential diagnosis are presented.

Fundus Autofluorescence Imaging in Best's Vitelliform Dystrophy

BACKGROUND

It is well known that with age lipofuscin accumulates in the retinal pigment epithelium (RPE). In many inherited macular dystrophies such as Best's disease abnormally high levels of lipofuscin were found by histopathological studies. In recent years, it has become possible to detect and image fundus autofluorescence in the living eye as an index of lipofuscin accumulation in the RPE. The aim of our study was to document the intrinsic fundus autofluorescence in patients with different stages of Best's disease and to correlate fundoscopic features with visual function in these patients.

METHODS

Images of fundus autofluorescence were obtained from 10 patients with Best's vitelliform dystrophy, using a Heidelberg Retina Angiograph (HRA). Argon laser light (488 nm) was used for illumination, and a wide-bandpass filter with a cutoff of 500 nm was inserted in front of the detector to obtain the autofluorescence images. Images were compared with fundus appearance and fluorescein angiograms as well as with visual acuity, colour vision, visual fields and electrophysiological recordings in these patients.

RESULTS

In initial stages of Best's disease, there were localised areas of hyperfluorescence centrally in the fovea, later being replaced by central hypofluorescence (atrophic) areas surrounded by hyperfluorescent rings. The evolution of autofluorescence pattern showed centrifugal spreading of retinal dysfunction from the centre towards periphery. Atrophic regions of the RPE were associated with low levels of background autofluorescence, lower visual acuity, abnormal colour vision (70% of patients), central scotomas (85% of patients) and poorer electrophysiological results (reduced PERG responses in 45% of patients with Best's disease).

CONCLUSIONS

Fundus autofluorescence imaging provides new information regarding the content and spatial distribution of RPE lipofuscin in eyes with Best's disease, which appears to correspond to retinal function. This may "in vivo" give important clues to the pathogenesis and progression of Best's disease in which non-invasive autofluorescence imaging may replace fluorescein angiography.

[Analysis of mutation of BIGH3 gene in Chinese patients with corneal dystrophies]

OBJECTIVE

To study whether Chinese patients with various corneal dystrophy carry mutations in BIGH3 gene.

METHODS

Genomic DNA was extracted from Chinese patients with Avellino corneal dystrophy (ACD, 10 cases), Reis-Bücklers corneal dystrophy (CDRB, 2 cases), granular corneal dystrophy (GCD, 3 cases) and 5 control subjects. The exons 4 and 12 of BIGH3 gene were amplified by PCR and the product was sequenced directly.

RESULTS

All 15 patients carried mutations in BIGH3 gene, R124H in 10 cases with ACD, R124L in 2 cases with CDRB and R555W in 3 cases with GCD.

CONCLUSIONS

Corneal lesions in all 15 Chinese patients clinically diagnosed with corneal dystrophies are caused by mutations in BIGH3 gene. Dose-effect analysis shows that corneal lesions are more severe in homozygous patients than those in heterozygous cases and that clinical manifestation of patients with R124L mutation is more severe than that of patients with R124H mutation.

[Corneal dystrophies in the light of modern molecular genetic research]

Modern methods of molecular genetics have resulted in new insights into the pathogenesis of corneal dystrophies which now require a new classification. Clinical evidence, the results of histopathological and electron-microscopical examinations, especially in cases of recurrence which reflect early disease, and the immunohistochemical analysis of the deposits have already aroused the suspicion that the "old" classification dividing the dystrophies into those of the epithelium, of the so-called anterior membrane, of the stroma and of the endothelium may no longer be adequate. The detection of the BIGH 3 gene which is mainly expressed in the corneal epithelium, and its gene product keratoepithelin, have led to the insight that the so-called anterior membrane dystrophies (Reis-Bücklers, Thiel-Behnke) as well as the more common "classical" stromal dystrophies (granular dystrophies Types I and II, lattice dystrophies Types I and IIIA) are caused by different mutations of the above mentioned BIGH3 gene and are thus to be regarded as epithelial in origin. Lattice dystrophy Type II is part of the Meretoja syndrome, a systemic amyloidosis, and is caused by a mutation of the gelsoline gene on chromosome 9 (9q34). Gelsoline is also predominantly expressed in the corneal epithelium. In addition, the responsible genes, their gene-products and the mutations are known for Meesmann's epithelial dystrophy and for the so-called gelatinous drop-like dystrophy, while in other dystrophies only the location on a certain chromosome can be given, namely: 16q22 for the macular dystrophy, 1p36 for the central crystalline dystrophy of Schnyder and 20p11.2-q11.2 for the congenital hereditary endothelial and for Schlichting's posterior polymorphous dystrophies. As the production rate of new results in molecular genetics is very fast, the proposed new classification can only be of preliminary character.

Corneal dystrophies in Japan

Recent advances in molecular genetics have increased our understanding of the role of genes. Four autosomal dominant corneal dystrophies (CDs); granular CD (GCD), Avellino CD (ACD), lattice CD (LCD), and Reis-Bücklers CD (RBCD) were mapped to the long arm of chromosome 5 (5q31). These four diseases were shown, in a Caucasian series, to result from different missense mutations in the TGFBI (BIGH3, keratoepithelin) gene. The same mutations were also detected in Japanese patients, from a different ethnic background. Gelatinous drop-like corneal dystrophy (GDLD), on the other hand, which was found in Japanese patients in 1914, is a rare autosomal recessive disorder characterized by corneal amyloidosis. Parents of the patients had a markedly higher frequency of consanguineous marriages than the general population. The gene responsible for GDLD, the membrane component, chromosome 1, surface marker 1 (M1S1) gene was mapped to the short arm of chromosome 1(1p). Four deleterious mutations in this gene were detected in Japanese patients. We review here additional studies on mutations of the TGFBI and M1S1 genes found in Japanese patients. In the TGFBI gene, nine different mutations were detected in Japanese patients with GCD, ACD, LCD, or RBCD. The codons R124 and R555 of the TGFBI gene were hotspots in Japanese patients, of whom many were ACD patients with the R124H mutation. New mutations responsible for LCD were detected in the TGFBI gene of patients with LCD, in addition to the P501T mutation in LCD type IIIA found earlier. These studies showed a clear genotype/phenotype correlation associated with the TGFBI gene. In the M1S1 gene, the Q118X mutation was the most common alteration, and a founder mutation in Japanese GDLD patients, as previously reported. Ninety-two percent of the mutated alleles were the Q118X.

Immunohistochemical classification of primary and recurrent macular corneal dystrophy in Germany: subclassification of immunophenotype I A using a novel keratan sulfate antibody

Macular corneal dystrophy (MCD) is an autosomal recessive disease characterized by abnormal deposition of glycosaminoglycans in corneal stroma, keratocytes, Descemet's membrane and corneal endothelium. According to the presence and distribution of sulfated keratan sulfate (KS)-epitopes in serum and cornea (using mAb 5-D-4), MCD can be classified into three immunophenotypes: type I, I A and II. The purpose of this study is to evaluate the immunophenotype of primary and recurrent MCD and to analyze the reactions of a novel KS-antibody in MCD corneas, which recognizes an epitope localized in the binding region of KS-chains to the core protein (mAb 3D12/H7). Indirect immunohistochemistry for KS (mAbs 3D12/H7 and 5-D-4) was performed on 44 corneas of 37 patients with MCD including two recurrences. Immunogold labeling was used to localize KS ultrastructurally within keratocytes. The serum concentration of KS (cKS) was determined in a serum antigen-inhibition assay. Immunohistochemically, no reaction was observed using mAb 5-D-4 in 18 corneas of 16 patients (43% of 37 patients; immunophenotype I). Positive reactions within single keratocytes but not in the stroma, were seen in 22 corneas of 17 patients (46% of 37 patients; immunophenotype I A) and positive reactions in keratocytes and extracellular stroma were found in four corneas of four patients (11% of 37 patients: immunophenotype II). For analysis of cKS a total of seven samples was available. Whereas in the samples of the five patients with immunophenotypes I and I A cKS was below the limit of detection, in the two sera from patients with immunophenotype II, cKS was normal (cKS = 1243 and 1380 nmol l(-1)). The two recurrences demonstrated immunophenotype II. Using mAb 3D12/H7, MCD immunophenotype I A can be further subclassified in type I A 1 (lacking reaction with mAb 3D12/H7 in keratocytes; 77%) and type I A 2 (positive reaction with mAb 3D12/H7 within keratocytes; 23%). MCD immunophenotype I A can not only be found in Saudi Arabia, but is as common as immunophenotype I in German patients. The only recurrences of MCD necessitating regrafting occurred in two patients with immunophenotype II possibly suggesting a higher risk for recurrence in this immunophenotype. The mAb 3D12/H7 allows a further subclassification of immunophenotype I A into type I A1 and 2. This points to a broader spectrum of MCD immunophenotypes and indirectly to a broader corneal proteoglycan pathology in MCD.

[Autosomal dominant inherited corneal dystrophies associated with TGFBI mutation]

BACKGROUND

Mutations of the transforming growth factor beta-induced (TGFBI) gene whose product is called keratoepithelin (KE) have been identified in 4 major autosomal dominantly inherited corneal dystrophies. The purpose of this study was to identify the mutations in Japanese patients with these dystrophies, and to investigate the nature of corneal deposits.

METHOD

Mutations of the TGFBI gene were screened by polymerase chain reaction (PCR) followed by direct sequencing of the PCR products in Japanese patients clinically diagnosed as having granular corneal dystrophy, Avellino corneal dystrophy, lattice corneal dystrophy, and Reis-Bücklers' dystrophy. Corneal specimens obtained from corneal transplants were analyzed by histochemistry (Masson trichrome and Congo red stains), immunohistochemistry, and western blotting using anti KE antibody. I reviewed papers about TGFBI gene mutations previously published.

RESULTS

The genotype/phenotype relationship of corneal dystrophies associated with mutations of the TGFBI gene is markedly evident. Avellino corneal dystrophy associated with the R 124 H mutation was the most common form of corneal stromal dystrophy in Japan. In Japan this dystrophy has been called granular corneal dystrophy up to now. Thiel-Behnke dystrophy (R 555 Q) has been also misdiagnosed as Reis-Bücklers' dystrophy. The original Reis-Bücklers' dystrophy is associated with R 124 L, which is compatible with superficial granular corneal dystrophy. Corneal deposits were associated with TGFBI products whose sizes were specific for their mutations.

CONCLUSIONS

Mutations of the gene resulted in different types of KE aggregation accompanied with characteristic changes of processing and metabolism. The classification of these diseases according to genetic pathogenesis may be more appropriate than the use of clinical or histological findings.

[Chromosome 5q31 linked corneal dystrophies: outline for a new classification]

The following article is an attempt to summarise the recent genetic findings in chromosome 5q31 corneal dystrophies. It also shows the remarkable correlation between genotype and phenotype characterising them. Basically, 6 main heterozygote mutations are responsible for 6 different phenotypes, corresponding to the following 4 histologic forms of corneal deposits: a) amyloid or lattice, b) granular, c) amyloid or lattice and granular, d) non-amyloid and non-granular (fibrous).

Macular corneal dystrophy type I and type II are caused by distinct mutations in a new sulphotransferase gene

Macular corneal dystrophy (MCD; MIM 217800) is an autosomal recessive hereditary disease in which progressive punctate opacities in the cornea result in bilateral loss of vision, eventually necessitating corneal transplantation. MCD is classified into two subtypes, type I and type II, defined by the respective absence and presence of sulphated keratan sulphate in the patient serum, although both types have clinically indistinguishable phenotypes. The gene responsible for MCD type I has been mapped to chromosome 16q22, and that responsible for MCD type II may involve the same locus. Here we identify a new carbohydrate sulphotransferase gene (CHST6), encoding an enzyme designated corneal N-acetylglucosamine-6-sulphotransferase (C-GlcNAc6ST), within the critical region of MCD type I. In MCD type I, we identified several mutations that may lead to inactivation of C-GlcNAc6ST within the coding region of CHST6. In MCD type II, we found large deletions and/or replacements caused by homologous recombination in the upstream region of CHST6. In situ hybridization analysis did not detect CHST6 transcripts in corneal epithelium in an MCD type II patient, suggesting that the mutations found in type II lead to loss of cornea-specific expression of CHST6.

Heterogeneity in granular corneal dystrophy: identification of three causative mutations in the TGFBI (BIGH3) gene-lessons for corneal amyloidogenesis

Six autosomal dominant corneal dystrophies are caused by mutations in the TGFBI (BIGH3) gene on chromosome 5q31: three types of lattice corneal dystrophy (LCD), including type I and type IIIA, granular, Avellino (ACD), and Reis-Bucklers. Initially an exact genotype-phenotype correlation was reported. We report three families, with differing clinical features, all presenting with "granular" corneal dystrophy. We analysed the TGFBI gene by SSCP analysis and direct sequencing in order to further assess the genotype-phenotype correlation. We describe three separate mutations in TGFBI: one novel, one initially described as causing ACD, and one previously described. The novel mutation, R124S, is at the identical position to the mutation causing LCD type I (CDL1). We review the clinical and histological phenotypes of the corneal dystrophies and hypothesize that the ability of a mutation to cause amyloid deposition depends on the location and nature of the mutation. In addition, we suggest that the classification of the granular corneal dystrophies be revised according to mutation type and that ACD should not be classified as a distinct morphological entity.

Coexistence of macular corneal dystrophy types I and II in a single sibship

BACKGROUND

Macular corneal dystrophy (MCD) is an inherited autosomal recessive disorder that has been subdivided into two primary immunophenotypes, MCD types I and II. The MCD type I gene has been localised previously to chromosome 16q22 and suggestive evidence provided that MCD type II gene is also linked to this region. Here an unusual family is reported where both MCD types I and II are found in a single sibship.

METHODS

Immunoreactivity to an anti-keratan sulphate monoclonal antibody (5-D-4) was evaluated in patients' serum and in corneal tissue obtained at keratoplasty. Chromosomal haplotypes were constructed using microsatellite repeat markers spanning the region of the MCD type I locus.

RESULTS

Immunological studies demonstrated that two of the affected siblings have MCD type II while one has MCD type I. Haplotype analysis suggests that all three affected sibs inherited one identical parental haplotype. However, the two MCD types differ in their alternative chromosome with both MCD type II children sharing an identical haplotype, different from their MCD type I sibling.

CONCLUSION

The findings in this study support the hypothesis that the genes for MCD types I and II co-localise to the same region of chromosome 16 and are likely to be due to allelic manifestations of the same abnormal gene.

[Type I lattice corneal dystrophy. Clinical and molecular genetic study of a large family]

BACKGROUND

Lattice corneal dystrophy type I is one of the frequent forms of stromal dystrophies following autosomal dominant inheritance. The beta-IG-h3 gene encoding keratoepithelin on the long arm of chromosome 5 has recently been described as disease gene for lattice corneal dystrophy type I as well as for three other corneal dystrophies with autosomal dominant pattern of inheritance.

PATIENTS AND METHODS

Ten family members in three generations of a large family with autosomal dominant lattice corneal dystrophy were analyzed clinically by slit-lamp biomicroscopy. Mutation analysis in the beta-IG-h3 gene was carried out at the mRNA level by RT-PCR and cDNA sequencing.

RESULTS

A heterozygous single-base substitution (417C-->T) in exon 4 of the beta-IG-h3 gene was detected predicting the replacement of arginine-124 by cysteine. Analysis of 10 family members showed perfect cosegregation of the mutation and lattice corneal dystrophy type I. The investigation excluded this mutation in one family member previously classified as potentially affected.

CONCLUSIONS

The investigation confirmed autosomal dominant inheritance with complete penetrance in the family described. The mutation 417C-->T has already been found earlier in another family of different geographic origin. These results suggest a mutation hot spot at position 417. In addition, no evidence of genetic heterogeneity of lattice corneal dystrophy type I was detected. Molecular genetic analysis (in conjunction with genetic counselling) therefore may be useful in routine diagnostics as the confirmation of the diagnosis by histological examination is possible only after keratoplasty. The common pathomechanism in lattice corneal dystrophy type I may facilitate development of new therapeutic concepts; the easy accessibility of the target organ may provide new possibilities e.g. for gene therapy.

Mutation hot spots in 5q31-linked corneal dystrophies

Mutations in the BIGH3 gene on chromosome 5q31 cause four distinct autosomal dominant diseases of the human cornea: granular (Groenouw type I), Reis-Bücklers, lattice type I, and Avellino corneal dystrophies. All four diseases are characterized by both progressive accumulation of corneal deposits and eventual loss of vision. We have identified a specific recurrent missense mutation for each type of dystrophy, in 10 independently ascertained families. Genotype analysis with microsatellite markers surrounding the BIGH3 locus was performed in these 10 families and in 5 families reported previously. The affected haplotype could be determined in 10 of the 15 families and was different in each family. These data indicate that R555W, R124C, and R124H mutations occurred independently in several ethnic groups and that these mutations do not reflect a putative founder effect. Furthermore, this study confirms the specific importance of the R124 and R555 amino acids in the pathogenesis of autosomal dominant corneal dystrophies linked to 5q.

Homogeneity of kerato-epithelin codon 124 mutations in Japanese patients with either of two types of corneal stromal dystrophy

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[Hereditary retinal diseases]

Hereditary retinal dystrophies can be subdivised into central (macular) and peripheral degenerations. Stargardt disease, Best disease, cone dystrophy and retinoschisis, affecting children or young adults, are the 4 commonest macular dystrophies. Retinitis pigmentosa, with primary affects photoreceptors, presents a wide clinical, genetic and molecular heterogeneity. It is certainly the most representative cause of peripheral degeneration. Recent advances in molecular biology allow a more complete clinical definition of these inheritable retinal diseases.

Macular flicker electroretinograms in Best vitelliform dystrophy

PURPOSE

The aim of this study was to evaluate the function of the neurosensory retina in Best vitelliform macular dystrophy (BMD) by recording the focal electroretinogram (ERG) fundamental and 2nd harmonic components, which are known to be dominated by receptoral and postreceptoral activity, respectively.

METHODS

FERGs were recorded in response to a uniform field (9 x 9 deg) flickered sinusoidally at either 8 Hz or 32 Hz (peak frequencies for the 2nd and fundamental harmonic, respectively). The fundamental component of the response to the 32-Hz stimulus and the 2nd harmonic of the response to the 8-Hz stimulus were measured in their amplitudes and phases. The fundamental-2nd harmonic amplitude ratio was taken as an index of the relative changes in the FERG components. Eleven patients with BMD and vitelliform stage macular lesions were evaluated. Results were compared with those obtained from 13 patients with Type 2 Stargardt macular dystrophy (STD) according to the Noble and Carr Classification, and 29 normal control subjects. Four BMD and four STD patients were also followed electrophysiologically over a 48 month period.

RESULTS

Compared to controls, BMD patients showed losses of both FERG fundamental and 2nd harmonic amplitudes, and an increase in the fundamental and increase in the fundamental-2nd harmonic ratio. STD patients also showed losses of both fundamental and 2nd harmonic, but the fundamental-2nd harmonic ratio was normal. In BMD patients, but not in those with STD, the fundamental amplitude tended to decrease over the follow-up period.

CONCLUSIONS

The results indicate that BMD involves neurosensory abnormalities early in the disease process. The increased fundamental-2nd harmonic ratio suggests that a postreceptoral dysfunction may be present in addition to that of photoreceptors. This differs from STD, where losses appear to affect primarily the receptoral retina. Receptoral losses in BMD may progress throughout the medium-term follow up.

[Pattern dystrophies and intrafamilial phenotypic variation]

BACKGROUND

Transmitted in an autosomal dominant fashion, the pattern dystrophies involve the retinal pigment epithelium and the external macular retina and are usually divided into four different entities. However, a progression from one form to another is possible, various forms may coexist in the same patient and a combination of different entities may be present in the same family.

CASE REPORTS

Two families (4 cases) are described, in which a butterfly dystrophy coexist with a vitelliform dystrophy or with a central atrophy. Whereas the vitelliform dystrophy is usually characterised by a unique centromacular lesion, a case of multiple lesions is described. The possible association with a neovascular membrane is also presented.

CONCLUSION

The coexistence of various forms of pattern dystrophies in a same family suggests a variable expression of a same genetic disorder. The presence of a centromacular atrophy in one patient demonstrates also that the spectrum of the disease is not limited to the four classic entities.

Schnyder crystalline dystrophy sine crystals. Recommendation for a revision of nomenclature

PURPOSE

To determine the percentage of patients with Schnyder crystal line dystrophy who had corneal crystal deposition.

METHODS

Thirty-three patients with Schnyder crystalline dystrophy were identified by the author since 1987. Each patient had a complete ophthalmic evaluation, including slit-lamp examination by the author.

RESULTS

Only 51% (17 of 33) of patients with Schnyder crystalline corneal dystrophy actually had clinical evidence of corneal crystalline deposits.

CONCLUSIONS

Because of the confusing nomenclature, many ophthalmologists presume that the presence of corneal crystals is an integral part of the diagnosis of Schnyder crystalline dystrophy. The clinician should be aware that despite the fact that the noncrystalline form of the dystrophy has been poorly recognized, it is equally common.

Delineation of a 1-cM region on distal 5q containing the locus for corneal dystrophies Groenouw type I and lattice type I and exclusion of the candidate genes SPARC and LOX

Granular Groenouw type I (CDGG1) and lattice type 1 (CDL1) corneal dystrophies are two distinct potentially blinding conditions. These two entities were recently mapped to a region on chromosome 5q. We have investigated 2 families of Swiss origin with CDGG1 and CDL1 by linkage analysis. Our data show a maximum lod score of 5.38 at theta = 0.00 for marker D5S393 in CDL1 and 4.17 at theta = 0.00 for D5S658 in CDGG1. When combined, these families show a maximum low score of 9.22 for D5S393 at theta = 0.00. This confirms previous reports. Furthermore, we describe a recombination centromeric to D5S399 in a member of the CDL1 family. Haplotype analysis in the 4 branches of the CDGG1 family demonstrated a common chromosomal region including D5S393 and D5S399 in all the affected members. By combining our data with previously reported mapping information and assuming that CDGG1 and CDL1 are allelic manifestations of the same gene, we can refine the location of the CDGG1/CDL1 gene to a 1-cM region on chromosome 5q. Using candidate genes in the 5q22-q32 interval, we investigated the possibility that mutations in the SPARC or LOX genes cause these corneal diseases. Several recombinations occurred between these two genes and CDGG1/CDL1 in our 2 families, thus excluding this hypothesis.

Posterior amorphous corneal dysgenesis

PURPOSE

Posterior amorphous corneal dysgenesis is a rare disorder previously described in only four families. We expanded the spectrum of findings and updated the classification by adding seven additional cases.

METHODS

Three index cases were identified during ophthalmic examination at the El Maghraby Eye Hospital and Eye Center in Jeddah, Saudi Arabia. We examined all available members of three families of different ethnic origin (Saudi Arabian, Egyptian, and Indian) and found seven cases of affected patients. Videokeratography and slit-lamp photomicrography were done in selected cases.

RESULTS

In all seven cases, the corneas showed bilateral, diffuse, sheetlike opacities in the posterior stroma, with extension to the corneoscleral limbus, and corneal thinning in the more severely affected eyes. The clinical findings included variations in corneal thickness noted by slit-lamp microscopy and ultrasonic pachymetry, cornea plana, marked corneal astigmatism, and progressive ectasia of the cornea.

CONCLUSIONS

Posterior amorphous corneal dysgenesis is characterized by gray sheetlike opacities in the posterior stroma. It occurs in many ethnic groups and exhibits a varied spectrum of clinical findings, including iridocorneal adhesions and cornea plana. We think the anatomic abnormalities of the cornea warrant classification as a corneal dysgenesis rather than as a dystrophy. Longitudinal studies of individual eyes and investigation of associated abnormalities in other pedigrees may help resolve this distinction.

Histopathologic and immunochemical features of lattice corneal dystrophy type III

We examined seven corneas from five patients with a new form of lattice corneal dystrophy (designated lattice corneal dystrophy type III) by light and electron microscopy. Numerous amyloid deposits were scattered throughout the corneal stroma, some of which were much larger than those usually observed in either lattice corneal dystrophy type I or II; these were located predominantly midway between the epithelium and the endothelium. Image analysis disclosed that the cross-sectional size of the large stromal amyloid deposits was significantly greater than those in age-matched patients with lattice corneal dystrophy type I. All patients had a discontinuous band of amyloid (15 to 25 micron wide) in the superficial stroma beneath Bowman's layer, which usually had only one or two small disruptions. Descemet's membrane and the endothelium were normal. The stromal deposits, which were composed of 10-nm diameter fibrils typical of amyloid, stained positively with Congo red after the histologic sections were pretreated with dilute potassium permanganate. Immunohistochemical studies on formalin-fixed, paraffin-embedded tissue indicated that only some deposits reacted weakly with antibodies to amyloid protein AA. The deposits stained positively with antibodies to protein AP and negatively with antibodies to kappa and lambda immunoglobulin light chains.

Clinical features of a newly recognized type of lattice corneal dystrophy

We examined five patients with an undescribed type of lattice corneal dystrophy. All patients were in the seventh to ninth decades of life and had developed decreasing vision late in life. None of the patients had suffered from recurrent epithelial erosions, there was no overt evidence of systemic amyloidosis, and the lattice lines were much thicker than those usually observed in lattice corneal dystrophy types I and II. Available pedigree data from two families of three patients indicated that the corneal disorder affected several siblings but not the parents or offspring. Two patients had no affected family members. There was no known consanguinity in any of the four families.

The honeycomb type of Reis-Bücklers' dystrophy of the cornea: biometrics and an interpretation

Corneal thickness increases with advancing age in patients with the honeycomb type of Reis-Bücklers' dystrophy, affecting visual acuity. A linear relationship is found between these parameters. Also, corneal sensitivity decreases with increasing corneal thickness. The latter may be an import factor in the decrease of ocular irritation later in life in these patients.

Lattice dystrophy type 1: a report of 8 families

Eight families with lattice corneal dystrophy are reported. The symptoms and signs are almost identical with the typical lattice corneal dystrophy type 1 in western countries. Lattice corneal dystrophy has been considered to be a rare disease until recently, but it might be a more common disorder. This is the first report of a large series of lattice corneal dystrophy in Japan.

Punctiform and polychromatic pre-Descemet's dominant corneal dystrophy

A new type of pre-Descemet's corneal dystrophy is described. The opacities are punctiform, polychromatic, of uniform size, and evenly distributed over the whole cornea. The diagnosis is made only by slit lamp because there is no visual impairment. The disease is hereditary and follows the autosomal mode of inheritance with a high percentage of penetrance, expressivity, and specificity in 4 successive generations, in which 8 affected members were observed among a total of 46.