Assignment of granular corneal dystrophy Groenouw type I (CDGG1) to chromosome 5q

Mutation update: TGFBI pathogenic and likely pathogenic variants in corneal dystrophies

Human transforming growth factor β-induced (TGFBI), is a gene responsible for various corneal dystrophies. TGFBI produces a protein called TGFBI, which is involved in cell adhesion and serves as a recognition sequence for integrins. An alteration in cell surface interactions could be the underlying cause for the progressive accumulation of extracellular deposits in different layers of the cornea with the resulting changes of refractive index and transparency. To this date, 69 different pathogenic or likely pathogenic variants in TGFBI have been identified in a heterozygous or homozygous state in various corneal dystrophies, including a novel variant reported here. All disease-associated variants were inherited as autosomal-dominant traits but one; this latter was inherited as an autosomal recessive trait. Most corneal dystrophy-associated variants are located at amino acids Arg124 and Arg555. To keep the list of corneal dystrophy-associated variant current, we generated a locus-specific database for TGFBI (http://databases.lovd.nl/shared/variants/TGFBI) containing all pathogenic and likely pathogenic variants reported so far. Non-disease-associated variants are described in specific databases, like gnomAD and ExAC but are not listed here. This article presents the most recent up-to-date list of disease-associated variants.

[Corneal dystrophies]

Degenerative or hereditary corneal diseases are sometimes difficult to discriminate. Corneal dystrophies affect approximately 0.09 % of the population. They are identified by the IC3D classification based on their phenotype, genotype and evidence gathered for their diagnosis. Practically, the ophthalmologist manages functional symptoms, such as recurrent erosions, visual loss and amblyopia, photophobia, foreign body sensation, and sometimes pain and aesthetic concerns. Medical treatments consist of drops to promote healing, ointments, hyperosmotic agents and bandage contact lenses. Less invasive surgical treatments are used as second line therapy (phototherapeutic keratectomy, lamellar keratectomy). More invasive procedures may eventually be utilized (lamellar or penetrating keratoplasty). Anterior lamellar or endothelial keratoplasty are now preferred to penetrating keratoplasty, although the latter still remains the only possible option in some cases. Some rare dystrophies require coordinated and comprehensive medical care.

Corneal dystrophies

Degenerative or hereditary corneal diseases are sometimes difficult to discriminate. Corneal dystrophies affect approximately 0.09% of the population. They are identified by the IC3D classification based on their phenotype, genotype and evidence gathered for their diagnosis. In practice, the ophthalmologist manages functional symptoms such as recurrent erosions, visual loss and amblyopia, photophobia, foreign body sensation, and sometimes pain and aesthetic concerns. Medical treatments consist of drops to promote healing, ointments, hyperosmotic agents and bandage contact lenses. Less invasive surgical treatments are used as second line therapy (phototherapeutic keratectomy, lamellar keratectomy). More invasive procedures may eventually be utilized (lamellar or penetrating keratoplasty). Anterior lamellar or endothelial keratoplasty are now preferred to penetrating keratoplasty, although the latter still remains the only possible option in some cases. Some rare dystrophies require coordinated and comprehensive medical care.

Granular corneal dystrophy: a novel approach to classification and treatment

PURPOSE

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

CASE REPORT

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

CONCLUSIONS

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

Establishment of a transgenic mouse model of corneal dystrophy overexpressing human BIGH3

This study aimed to establish a transgenic mouse model of corneal dystrophy (CD) overexpressing the human transforming growth factor, β-induced, 68 kDa (TGFBI, also known as BIGH3) gene. A purified and linearized recombinant plasmid carrying the expression cassette BIGH3‑IRES‑EGFP was microinjected into the pronuclei of C57BL/6J mouse fertilized eggs under the control of the phosphoglycerate kinase (PGK) promoter. The expression of human BIGH3 in the transgenic mice was confirmed by PCR using DNA extracted from tail tissue. Four founder transgenic mice were identified by PCR and the increased expression of BIGH3 was observed in the corneas of the transgenic mice by RT-PCR and western blot analysis. The abnormal corneas with central opacity were observed in the transgenic mice by corneal photography. We concluded that the exogenous gene, BIGH3, was integrated successfully into the mouse genome through microinjection. In addition, the phenotype observed in this BIGH3 transgenic mouse model was similar to CD. Therefore, this transgenic model may prove useful in the investigation of the pathogenesis of CD.

A unique TGFBI protein in granular corneal dystrophy types 1 and 2

PURPOSE

Types 1 and 2 granular corneal dystrophies (GCD) are primarily associated with accumulation of the R555W and R124H mutant transforming growth factor β-inducible proteins (TGFBIp) in corneal stroma, respectively. However, specific components of TGFBIp responsible for granular deposits have not been delineated. This study was undertaken to identify the mutant TGFBIp components potentially responsible for GCD.

METHODS

Recombinant TGFBIp of wild-type (WT) and three mutants, R124C, R124H, and R555W, were generated in HEK293FT cells. WT and TGFBIp mutants were collected from cell lysates. Immunoblot analyses were performed with five different antibodies directed against various regions of WT TGFBIp.

RESULTS

WT and TGFBIp mutants showed differential reactivities with these antibodies. In contrast to our prior observation in purified WT and TGFBIp mutants, TGFBIp from cell lysates were less prone to polymerize. A unique 35 kD fragment was detected in cell lysates of R555W and R124H, but not in those of WT or R124C, by a commercial antibody raised against amino acids (a.a.) 199-406 of TGFBIp.

CONCLUSIONS

Monomeric and polymeric WT and TGFBIp mutants were observed in vitro. The 35 kD fragment found only in R555W and R124H, but not in WT and R124C cell lysates, is likely a degraded TGFBIp derived from the central domain of these mutants and this fragment may be contributory to the nonamyloid granular deposits observed in GCD 1 and 2.

Confocal microscopy and optical coherence tomography imaging of hereditary granular dystrophy

OBJECTIVES

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

CASE REPORT

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

RESULTS

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

CONCLUSIONS

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

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.

Mutation screening of TGFBI in two Iranian Avellino corneal dystrophy pedigrees

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

A clinical and molecular genetic study of autosomal-dominant stromal corneal dystrophy in British population

AIMS

To identify the underlying mutations in our British families and sporadic patients with different types of corneal dystrophies (CDs) and to establish a phenotype-genotype correlation.

METHODS

Twenty-nine patients, 9 sporadic and 20 patients from 7 families were subjected to both clinical and genetic examination. Slit lamp examination was performed for all patients who participated in the study to assess their corneal phenotype. Genomic DNA was extracted from 10 ml venous blood, and the BIGH3 gene was amplified exon by exon to perform heteroduplex analysis. Exons that displayed double bands were then analysed by direct bi-directional sequencing and restriction digest analyses.

RESULTS

Clinically our patients showed three distinct phenotypes of CD: 16 with Thiel-Behnke corneal dystrophy or corneal dystrophy of Bowman layer type 2 (CDB2), 8 with granular CD (GCD), and 5 with lattice CD type I (LCDI). Three different missense mutations have been detected in the coding region of BIGH3 gene, R555Q, in 16 CDB2 patients, R555W in 8 GCD patients, and R124C in 5 LCDI patients. These mutations were the same as to those previously reported in patients from other ethnic origins. Also,we identified seven nucleotide substitutions that did not change the amino acid sequence of the encoded protein of which four were novel.

CONCLUSIONS

In our patients of British origin, each phenotype of CD has been linked to a particular point mutation of the BIGH3 gene. Our study also highlights the importance of codons 124 and 555 as mutation hot spots in the BIGH3 gene in the British population.

Mapping of hereditary trichilemmal cyst (TRICY1) to chromosome 3p24-p21.2 and exclusion of beta-CATENIN and MLH1

Trichilemmal cysts (also named pilar cyst) derived from the outer root sheath of the deeper parts of the hair follicle can segregate dominantly, and are caused by a yet unknown gene. In order to identify candidate genes for this trait we have ascertained a Danish family with 38 persons (11 affected), and carried out a genome wide scan with 580 DNA micro-satellite markers to identify the locus for a gene, which we termed TRICY1 (for trichilemmal cysts). We found tight linkage to D3S1277 (Z = 4.63; theta(M = F) = 0.00), with flanking markers D3S2432 (Z = 1.59; theta(M = F) = 0.08), and D3S3685 (Z = 2.69; theta(M = F) = 0.08) spanning 10.3 Mb on chromosome 3p24-p21.2. We sequenced two candidate genes previously reported in inherited hair defects, CTNNB1 and MLH1 but failed to detect mutations in exons and intron-exon bounders.

Recurrence of corneal dystrophy resulting from an R124H Big-h3 mutation after phototherapeutic keratectomy

PURPOSE

The purpose of the study was to investigate the recurrence-free interval after phototherapeutic keratectomy (PTK) in patients with corneal dystrophies resulting from an Arg124His (R124H) mutation of the Big-h3 gene.

METHODS

Patients with corneal dystrophy resulting from a genetically confirmed Big-h3 R124H mutation were examined with a slit lamp. The patients were divided into two groups on the basis of the mutation genotype, and the recurrence-free interval was analyzed.

RESULTS

In the 4 eyes of 3 homozygous patients, the mean (+/- standard deviation [SD]) recurrence-free interval was 9.5 +/- 3.1 months, whereas in the 7 eyes of 4 heterozygous patients it was 38.4 +/- 6.2 months. The former interval was statistically shorter than the latter (Kaplan-Meier survival analysis with log-rank test, p = 0.004).

CONCLUSIONS

These results strongly suggest that the mutation genotype of Big-h3 gene determined the recurrence-free interval as well as the clinical picture after PTK. Therefore, PTK should be considered for patients with Big-h3 R124H corneal dystrophy, on the basis of the expected recurrence-free interval deduced from molecular analysis of the zygosity of the Big-h3 R124H mutation.

Granular corneal dystrophy: slitlamp biomicroscopic appearances in three generations of patients

PURPOSE

The purpose of this case series is to show photographically the varying clinical appearance of granular corneal dystrophy in three generations of one family and to review the genetic basis of this and related conditions.

CASE SERIES

We present cases for four affected individuals along with slitlamp biomicroscopic photographs.

DISCUSSION

A review of the photographs and the literature suggests that the abnormal keratoepithelin first appears in the superficial cornea as faint subepithelial opacities. With time, these become arranged in the curved lines of a vortex pattern, after which the deposits become scattered in no particular pattern and at all levels of the cornea. In this family, corneal erosions are a regular feature. Mutations of the gene coding for keratoepithelin (beta ig-h3) may give rise to variable clinical manifestations.

BIGH3 gene analysis in the differential diagnosis of corneal dystrophies

PURPOSE

To identify the mutation in the keratoepithelin gene for proper diagnosis of granular corneal dystrophies.

METHODS

Four generations of a single family with corneal dystrophy were analyzed. Fourteen family members were examined and 11 were found to be affected by clinical evaluation. Genetic DNA was extracted from proband's leukocytes for molecular analysis. Exons 4 and 12 of the BIGH3 gene were amplified then directly sequenced.

RESULTS

The clinical appearance of corneas consisted of grayish white granules with sharp borders, fine dots, and radial lines in the superficial part of the central corneal stroma, which resembles granular and Avellino corneal dystrophies. Performing BIGH3 gene analysis, we observed a C-to-T transition at position 1710 (CGG to TGG) producing R555W mutation, which is a hot spot for granular corneal dystrophy.

CONCLUSION

Direct clinical examination may be insignificant in the proper diagnosis of corneal dystrophies, and molecular genetic approach may be required.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Granular corneal dystrophy with homozygous mutations in the kerato-epithelin gene

PURPOSE

To report a family with several members affected with granular corneal dystrophy Groenouw type 1. Three members of the family were affected with a severe placoid type of corneal dystrophy. To determine the relationship between gene mutations and phenotypic variations of the disease, we analyzed the kerato-epithelin gene.

METHODS

The pedigree included a consanguineous marriage of two affected individuals. The three family members affected with a severe form of corneal dystrophy were offspring of these parents. However, the phenotype of other affected family members was typical granular corneal dystrophy. We isolated genomic DNA from leukocytes of the family members. Exons of the keratoepithelin gene were amplified by the polymerase chain reaction and were analyzed using the single-strand conformation polymorphism technique. Mutations were identified by direct sequencing method and restriction digestion analysis.

RESULTS

The three severely affected family members exhibited homozygous mutations at codon 555 (arginine to tryptophan) in the keratoepithelin gene, whereas those with typical granular corneal dystrophy had the heterozygous mutation at the same codon. Unaffected family members did not have the mutation.

CONCLUSIONS

We determined that the severe phenotype of granular corneal dystrophy is caused by homozygous mutations in the kerato-epithelin gene. Clinical manifestation of the severe phenotype is a placoid type of corneal dystrophy and early recurrence after surgery. Granular corneal dystrophy appears to be the first ophthalmic disease in which homozygosity for a dominant allele has been genetically identified.

Kerato-epithelin mutations in four 5q31-linked corneal dystrophies

Granular dystrophy Groenouw type I (CDGG1), Reis-Bücklers (CDRB), lattice type I (CDL1) and Avellino (ACD) are four 5q31-linked human autosomal dominant corneal dystrophies. Clinically, they show progressive opacification of the cornea leading to severe visual handicap. The nature of the deposits remains unknown in spite of amyloid aetiology ascribed to the last two. We generated a YAC contig of the linked region and, following cDNA selection, recovered the beta ig-h3 gene. In six affected families we identified missense mutations. All detected mutations occurred at the CpG dinucleotide of two arginine codons: R555W in one CDGG1, R555Q in one CDRB, R124C in two CDL1 and R124H in two ACD families. This suggests, as the last two diseases are characterized by amyloid deposits, that R124 mutated kerato-epithelin (the product of beta ig-h3) forms amyloidogenic intermediates that precipitate in the cornea. Our data establish a common molecular origin for the 5q31-linked corneal dystrophies.

Linkage study between manic-depressive illness and chromosome 21

Chromosome 21, of interest as potentially containing a disease gene for manic-depressive illness as possible evidence for a gene pre-disposing to affective disorder, has recently been reported in a single large family as well as samples of families. The present study investigates for linkage between manic-depressive illness and markers covering the long arm of chromosome 21 in two manic-depressive families, using ten microsatellite polymorphisms as markers. No conclusive evidence for a disease gene on the long arm of chromosome 21 was found. Assuming either a dominant or recessive mode of inheritance, close linkage to the marker PFKL, which has been reported as possibly linked to affective disorder, seems unlikely in the families studied here. PFKL and more telomeric markers yielded small positive lod scores at higher recombination fractions in the largest family, and small positive lod scores at lower recombination fractions in the affected-only analyses in the smallest family.

Mapping of Reis-Bücklers' corneal dystrophy to chromosome 5q

PURPOSE

Recently several autosomal dominant corneal stromal dystrophies have been mapped to chromosome 5q. Therefore, we tested whether Reis-Bücklers' corneal dystrophy, an autosomal dominant trait, was also linked to the same region.

METHODS

Five generations of a single family with Reis-Bücklers' corneal dystrophy were ascertained. Twenty-two family members were examined, and 11 were found to be affected. Blood was obtained for genetic linkage analysis.

RESULTS

Several genetic markers on chromosome 5q were strongly suggestive of linkage or confirmed linkage (LOD score > 3.0). Multipoint analysis generated a maximum LOD score of 4.25 between D5S414 and IL-9.

CONCLUSIONS

Reis-Bücklers', lattice type 1, Avillino, and granular corneal dystrophies all map to the same genetic locus. This suggests that one of the following might be true: (1) that a corneal gene family exists in this region; (2) that these corneal dystrophies represent allelic heterogeneity (that is, different mutations within the same gene manifest as different phenotypes); or (3) that these are all the same disease.

Linkage analysis between manic-depressive illness and markers on the long arm of chromosome 11

The long arm of chromosome 11 is one of the most interesting regions in the search for major genes involved in the etiology of manic-depressive illness. Several candidate genes have been identified, including the gene encoding the dopamine D2 receptor, the M1 muscarinic receptor, and porfobillinogen deaminase. Furthermore, different families with co-segregation of psychiatric illness and structural chromosome abnormalities involving regions 11q21, 11q22.3, and 11q25 have been reported. Using narrow as well as broad phenotypic models, conservative genetic parameters, models with dominant or recessive modes of inheritance, and various methods to reduce misclassification, the present study did not find evidence for a major gene causing manic-depressive illness on the long arm of chromosome 11. In the broader phenotypic models multi-point analyses excluded at least 11q14 to 11q23.3, approximately 60 cM, even in one large family. Assuming homogeneity close linkage to DRD2 was excluded for all dominant models, and also in the affecteds-only analyses in the large family alone.

Assignment of dominant inherited nocturnal enuresis (ENUR1) to chromosome 13q

Nocturnal enuresis, or nightly bedwetting in children more than seven years of age affects about 10% of seven-year-old children, with a wide range of frequencies between populations. The affliction is often linked to major social maladjustments and occupies considerable time in general practice. From the age of seven there is a spontaneous cure rate of 15% per year, such that few remain affected after the age of 16 years. There are two types of nocturnal enuresis: type I (PEN1, primary) with at least three nightly episodes in children above seven years, where the child has always had the disorder and type II (secondary) where the child has been dry for at least six months, but enuresis has recurred. Among some 400 Danish, mostly three-generation families, we have found 17 families with nocturnal enuresis. Eleven of these family had type I nocturnal enuresis (PEN1) that appeared to follow an autosomal dominant mode of inheritance with penetrance above 90%. We now describe strong evidence of linkage with the DNA polymorphisms D13S291 (Z = 3.55; theta M = F = 0.07) and D13S263 (Z = 2.67; theta M = F = 0.08). Multipoint analysis indicates that these markers flank the disease locus at chromosome 13q13-q14.3.