Variant lattice corneal dystrophy associated with compound heterozygous mutations in theTGFBIgene

Mini-Review: Clinical Features and Management of Granular Corneal Dystrophy Type 2

Granular corneal dystrophy type 2 (GCD2) is an autosomal dominant corneal stromal dystrophy that is caused by p.Arg124His mutation of transforming growth factor β induced (TGFBI) gene. It is characterized by well demarcated granular shaped opacities in central anterior stroma and as the disease progresses, extrusion of the deposits results in ocular pain due to corneal epithelial erosion. Also, diffuse corneal haze which appears late, causes decrease in visual acuity. The prevalence of GCD2 is high in East Asia including Korea. Homozygous patients show a severe phenotype from an early age, and the heterozygote phenotype varies among patients, depending on several types of compound heterozygous TGFBI mutations. In the initial stage, conservative treatments such as artificial tears, antibiotic eye drops, and bandage contact lenses are used to treat corneal erosion. Different surgical methods are used depending on the depth and extent of the stromal deposits. Phototherapeutic keratectomy removes anterior opacities and is advantageous in terms of its applicability and repeatability. For deeper lesions, deep anterior lamellar keratoplasty can be used as the endothelial layer is not always affected. Recurrence following these treatments are reported within a wide range of rates in different studies due to varying definition of recurrence and follow-up period. In patients who have undergone corneal laser vision-correction surgeries such as photorefractive keratectomy, LASEK, or LASIK including SMILE surgery, corneal opacity exacerbates rapidly with severe deterioration of visual acuity. Further investigations on new treatments of GCD2 are necessary.

Mutation analysis of the TGFBI gene in pedigrees of lattice corneal dystrophy in Eastern China

BACKGROUND

To delineate the mutations of the TGFBI gene in Eastern China by whole-exome sequencing (WES) in eight Chinese families with lattice corneal dystrophy (LCD).

MATERIALS AND METHODS

This retrospective study included eight families with LCD from Eastern China. Clinical features were examined using slit-lamp examination, anterior segment optical coherence tomography, and in vivo confocal microscopy. Peripheral blood samples of probands were collected for WES, and saliva samples from family members were collected for TGFBI screening using Sanger sequencing. The physicochemical effects of mutations were investigated using bioinformatics tools.

RESULTS

Family 1 presented a classic LCD I with a p.R124C mutation of the TGFBI gene, while the other seven families were diagnosed with LCD IIIA. Six of the seven LCD IIIA families had heterozygous single-gene mutations (p.A546D, p.L565 H, p.T621P), and one had a compound heterozygous (cis) mutation (p.P501T and p.N622 H). The mutation of p.L565 H was the first time of integrated family report in contrast to the cases reported in 2019, and the p.T621P mutation was first reported in a Chinese population. Notably, the family with the compound mutation was associated with an obvious early-onset (in the 2nd decade of life) compared to the LCD IIIA patients with each single mutation (p.P501T or p.N622 H) showing late-onset (in the 7th decade of life).

CONCLUSIONS

WES is efficient for the genomic testing of LCD and genetic relationship identification in different families with the same mutated gene. We identified a compound heterozygous mutation (p.P501T and p.N622 H) and two mutations (p.T621P and p.L565 H) uncommon in China.

Compound heterozygous mutations in TGFBI cause a severe phenotype of granular corneal dystrophy type 2

We investigated the clinical and genetic features of patients with severe phenotype of granular corneal dystrophy type 2 (GCD2) associated with compound heterozygosity in the transforming growth factor-β-induced (TGFBI) gene. Patients with severe GCD2 underwent ophthalmic examination (best-corrected visual acuity test, intraocular pressure measurement, slit-lamp examination, and slit-lamp photograph analysis) and direct Sanger sequencing of whole-TGFBI. The patient’s family was tested to determine the pedigrees. Five novel mutations (p.(His174Asp), p.(Ile247Asn), p.(Tyr88Cys), p.(Arg257Pro), and p.(Tyr468*)) and two known mutations (p.(Asn544Ser) and p.(Arg179*)) in TGFBI were identified, along with p.(Arg124His), in the patients. Trans-phase of TGFBI second mutations was confirmed by pedigree analysis. Multiple, extensive discoid granular, and increased linear deposits were observed in the probands carrying p.(Arg124His) and other nonsense mutations. Some patients who had undergone phototherapeutic keratectomy experienced rapid recurrence (p.(Ile247Asn) and p.(Asn544Ser)); however, the cornea was well-maintained in a patient who underwent deep anterior lamellar keratoplasty (p.(Ile247Asn)). Thus, compound heterozygosity of TGFBI is associated with the phenotypic variability of TGFBI corneal dystrophies, suggesting that identifying TGFBI second mutations may be vital in patients with extraordinarily severe phenotypes. Our findings indicate the necessity for a more precise observation of genotype–phenotype correlation and additional care when treating TGFBI corneal dystrophies.

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

IMPORTANCE

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

BACKGROUND

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

DESIGN

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

PARTICIPANTS

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

METHODS

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

MAIN OUTCOME MEASURES

p.(L558P) variant of TGFBI gene.

RESULTS

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

CONCLUSIONS AND RELEVANCE

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

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.

Impaired Autophagic Degradation of Transforming Growth Factor-β-Induced Protein by Macrophages in Lattice Corneal Dystrophy

Purpose

Lattice corneal dystrophy (LCD) is related to the denaturation of transforming growth factor-β-induced protein (TGFBIp). Autophagic degradation of the denatured proteins by macrophages is one pathway to remove the denatured proteins. Thus, we investigated the role of autophagy in the degradation of mutant (MU) TGFBIp in macrophages.

Methods

Corneas from participants were observed by slit-lamp photography and subjected to histopathologic and genetic analysis. Wild-type (WT) and MU TGFBIp were recombined and expressed. Macrophages from MU participants were isolated and cocultured with the recombinant TGFBIp. Colocalization of the two molecules was observed by immunofluorescent microscopy. Enzyme-linked immunosorbent assay, Western blotting, and flow cytometry were used to detect changes in molecule expression related to the phenotype and autophagy process.

Results

Fourteen members from a family of 25 were identified as LCD sufferers. Significant TGFBIp aggregates and macrophage infiltration were found only in the corneas of LCD sufferers. Marker accumulation of TGFBIp was found in macrophages exposed to MU TGFBIp even at 5 hours after MU TGFBIp was withdrawn. High expressions of CD68 and CD36 were found in macrophages exposed to WT TGFBIp, but not to MU TGFBIp. Impaired autophagic flux due to defective autophagosome fusion to lysosomes was found in macrophages exposed to MU TGFBIp. Blockage of the autophagic process suppressed the expression of CD68 and CD36 in macrophages exposed to WT TGFBIp to levels similar to those found in macrophages exposed to MU TGFBIp.

Conclusions

Our results suggested that reversion of the defective autophagic process in macrophages may be a therapeutic strategy for patients with LCD.

Transforming growth factor β induced mutation-associated phenotype in a Chinese family exhibiting lattice corneal dystrophy

Lattice corneal dystrophy type I (LCDI) is associated with a large number of missense mutations in the transforming growth factor β induced (TGFBI) gene. The aim of the present study was to analyze TGFBI mutation in a Chinese family with LCDI, and to describe the clinical features and phenotype-genotype correlation within this family. Three generations of this family with LCDI were enrolled in the current study. Complete ophthalmic examinations were performed on all family members and mutation screenings of the coding regions of TGFBI were analyzed using a direct sequencing method. All family members underwent slit-lamp examination, and two patients and one of normal members in the family were evaluated by laser scanning in vivo confocal microscopy. A single heterozygous c.370C>T (p.R124C) mutation was identified in exon 4 of the TGFBI gene in five affected individuals, but not in the other family members and 400 normal control subjects. The affected members exhibited similar clinical features of LCDI, except that patient III:5 presented with mild symptoms. Confocal microscopy in vivo examination demonstrated that the proband (II:2) and his affected niece (III:4) had disruptions in multiple corneal layers, including the basal epithelial cells, stroma cells and Bowman's membrane. Thus, the R124C mutation in the TGFBI gene was identified in a Chinese family with LCDI. These results characterized the clinical features and revealed a genotype-associated phenotype in this family, which may contribute to understanding the pathogenesis of LCDI.

Vortex Pattern of Corneal Deposits in Granular Corneal Dystrophy Associated With the p.(Arg555Trp) Mutation in TGFBI

PURPOSE

To describe 2 unrelated families with multiple members demonstrating a less commonly recognized vortex pattern of corneal deposits confirmed to be granular corneal dystrophy type 1 (GCD1) after identification of the p.(Arg555Trp) mutation in the transforming growth factor β-induced gene (TGFBI).

METHODS

A slit-lamp examination was performed on individuals from 2 families, one of Mexican descent and a second of Italian descent. After DNA extraction from affected individuals and their unaffected relatives, TGFBI screening was performed.

RESULTS

Eight of 20 individuals in the Mexican family and 20 of 55 in the Italian family demonstrated corneal stromal opacities. Seven of the 8 affected individuals in the Mexican family and 4 of the 20 affected individuals in the Italian family demonstrated a phenotype characterized by a "sea fan" or vortex pattern of superficial stromal corneal deposits originating from the inferior aspect of the cornea. Screening of TGFBI in both families revealed a heterozygous missense mutation [p.(Arg555Trp)] in exon 12, confirming the diagnosis of GCD1.

CONCLUSIONS

Our findings demonstrate that GCD1 may present with a vortex pattern of anterior stromal deposits. Although this pattern of dystrophic deposits is not recognized by clinicians as a typical phenotype of GCD1, it is consistent with the production of the majority of the TGFBI protein by the corneal epithelium.