CTG18.1 Expansion in TCF4 Among African Americans With Fuchs' Corneal Dystrophy

Change in Visual Acuity of Patients With Fuchs Endothelial Corneal Dystrophy Over 1 Year

PURPOSE

To determine whether the clinical and paraclinical course of Fuchs endothelial corneal dystrophy (FECD) over 1 year is related to the extent of triplet repetition in the transcription factor 4 (TCF4) gene.

METHODS

A prospective study with a 1-year follow-up was conducted. A total of 104 patients (160 eyes) with FECD and an equivalent number of age- and sex-matched control subjects without FECD were included. At inclusion, the corneas were graded using the modified Krachmer grade (KG) and patients were genotyped for the number of trinucleotide repeats (TNRs) in the TCF4 gene by the short tandem repeat assay. Visual acuity, Scheimpflug tomographic features, and the Visual Function and Corneal Health Status using a visual disability instrument were measured on 2 visits at 1-year intervals.

RESULTS

KGs ranged from 1 to 6, and 46% of eyes had grades 1 to 4. 71% of the patients harbored TNR expansion (>40) versus 13% in control subjects ( P < 0.001). Severity at inclusion was higher in the presence of TNR expansion when considering eyes independently (mean grade ±SD, 4.08 ± 1.42) without TNR expansion and 4.66 ± 1.27 with TNR expansion ( P = 0.024). In 1 year, the ETDRS score significantly decreased by -2.97 (95% confidence interval -4.69 to -1.26, P = 0.001) and the ETDRS score with glare by -4.25 (95% confidence interval -6.22 to -2.27, P < 10 -5 ). There was no relationship between the rate of decline and TNR expansion or KG. Central corneal thickness and Visual Function and Corneal Health Status scores did not significantly vary.

CONCLUSIONS

It is possible to measure a subtle progression of FECD over a period as short as 1 year. We did not find a relationship between the presence of TNR expansion and the speed of deterioration over 1 year. This work should facilitate the design of future clinical trials on FECD.

Seeing in Color: Inclusion and Characterization of Hereditary Eye Disease in African Americans

Purpose

Hereditary eye diseases (HEDs) are individually rare but affect millions globally. The era of molecular genetics has ushered major advances in the study of these disorders; however, the inclusivity and population diversity of this research is unknown. Questions on the accuracy and applicability of these findings in diverse populations, especially African American patients, came up consistently during counselling sessions. This also raised the possibility of missed opportunities for broader understanding of these rare diseases. We conducted a literature review to measure the representation of African Americans in genomic research surrounding nine HEDs.

Methods

A detailed literature search using a predetermined set of search terms for each of nine HED categories was performed across PubMed, Embase, Web of Science, and Scopus focusing on studies published between Jan 1990 and July 2021. Predetermined inclusion criteria were applied to filter the sources.

Results

We identified 46 studies clearly reporting HED characterization in African Americans. Analysis of these inclusive studies revealed unique findings demonstrating the known usefulness of including diverse cohorts in genomics research.

Conclusions

HED characterization in diverse participants, specifically African Americans, is identified as a knowledge gap area. Genomic research is more applicable to patients when conducted in populations that share their ancestral background. Greater inclusion of African Americans in ophthalmic genetics research is a scientific imperative and a needed step in the pursuit of the best possible patient care for populations of all ancestries.

Translational Relevance

This work reveals gaps in genomic research in African Americans with HEDs.

A multi-ancestry GWAS of Fuchs corneal dystrophy highlights the contributions of laminins, collagen, and endothelial cell regulation

Fuchs endothelial corneal dystrophy (FECD) is a leading indication for corneal transplantation, but its molecular etiology remains poorly understood. We performed genome-wide association studies (GWAS) of FECD in the Million Veteran Program followed by multi-ancestry meta-analysis with the previous largest FECD GWAS, for a total of 3970 cases and 333,794 controls. We confirm the previous four loci, and identify eight novel loci: SSBP3, THSD7A, LAMB1, PIDD1, RORA, HS3ST3B1, LAMA5, and COL18A1. We further confirm the TCF4 locus in GWAS for admixed African and Hispanic/Latino ancestries and show an enrichment of European-ancestry haplotypes at TCF4 in FECD cases. Among the novel associations are low frequency missense variants in laminin genes LAMA5 and LAMB1 which, together with previously reported LAMC1, form laminin-511 (LM511). AlphaFold 2 protein modeling, validated through homology, suggests that mutations at LAMA5 and LAMB1 may destabilize LM511 by altering inter-domain interactions or extracellular matrix binding. Finally, phenome-wide association scans and colocalization analyses suggest that the TCF4 CTG18.1 trinucleotide repeat expansion leads to dysregulation of ion transport in the corneal endothelium and has pleiotropic effects on renal function.

Systematic Review of the Diagnostic Criteria and Severity Classification for Fuchs Endothelial Corneal Dystrophy

PURPOSE

There are no defined diagnostic criteria and severity classification for Fuchs endothelial corneal dystrophy (FECD), which are required for objective standardized assessments. Therefore, we performed a systematic literature review of the current diagnosis and severity classification of FECD.

METHODS

We searched the Ovid MEDLINE and Web of Science databases for studies published until January 13, 2021. We excluded review articles, conference abstracts, editorials, case reports with <5 patients, and letters.

RESULTS

Among 468 articles identified, we excluded 173 and 165 articles in the first and second screenings, respectively. Among the 130 included articles, 61 (47%) and 99 (76%) mentioned the diagnostic criteria for FECD and described its severity classification, respectively. Regarding diagnosis, slitlamp microscope alone was the most frequently used device in 31 (51%) of 61 articles. Regarding diagnostic findings, corneal guttae alone was the most common parameter [adopted in 23 articles (38%)]. Regarding severity classification, slitlamp microscopes were used in 88 articles (89%). The original or modified Krachmer grading scale was used in 77 articles (78%), followed by Adami's classification in six (6%). Specular microscopes or Scheimpflug tomography were used in four articles (4%) and anterior segment optical coherence tomography in one (1%).

CONCLUSIONS

FECD is globally diagnosed by the corneal guttae using slitlamp examination, and its severity is predominantly determined by the original or modified Krachmer grading scale. Objective severity grading using Scheimpflug or anterior segment optical coherence tomography can be applied in the future innovative therapies such as cell injection therapy or novel small molecules.

Association Between Fuchs Endothelial Corneal Dystrophy, Diabetes Mellitus, and Multimorbidity

PURPOSE

The aim of this study was to assess risk for demographic variables and other health conditions that are associated with Fuchs endothelial corneal dystrophy (FECD).

METHODS

We developed a FECD case-control algorithm based on structured electronic health record data and confirmed accuracy by individual review of charts at 3 Veterans Affairs (VA) Medical Centers. This algorithm was applied to the Department of VA Million Veteran Program cohort from whom sex, genetic ancestry, comorbidities, diagnostic phecodes, and laboratory values were extracted. Single-variable and multiple variable logistic regression models were used to determine the association of these risk factors with FECD diagnosis.

RESULTS

Being a FECD case was associated with female sex, European genetic ancestry, and a greater number of comorbidities. Of 1417 diagnostic phecodes evaluated, 213 had a significant association with FECD, falling in both ocular and nonocular conditions, including diabetes mellitus (DM). Five of 69 laboratory values were associated with FECD, with the direction of change for 4 being consistent with DM. Insulin dependency and type 1 DM raised risk to a greater degree than type 2 DM, like other microvascular diabetic complications.

CONCLUSIONS

Female sex, European ancestry, and multimorbidity increased FECD risk. Endocrine/metabolic clinic encounter codes and altered patterns of laboratory values support DM increasing FECD risk. Our results evoke a threshold model in which the FECD phenotype is intensified by DM and potentially other health conditions that alter corneal physiology. Further studies to better understand the relationship between FECD and DM are indicated and may help identify opportunities for slowing FECD progression.

Multi-ancestry GWAS of Fuchs corneal dystrophy highlights roles of laminins, collagen, and endothelial cell regulation

Fuchs endothelial corneal dystrophy (FECD) is a leading indication for corneal transplantation, but its molecular pathophysiology remains poorly understood. We performed genome-wide association studies (GWAS) of FECD in the Million Veteran Program (MVP) and meta-analyzed with the previous largest FECD GWAS, finding twelve significant loci (eight novel). We further confirmed the TCF4 locus in admixed African and Hispanic/Latino ancestries, and found an enrichment of European-ancestry haplotypes at TCF4 in FECD cases. Among the novel associations are low frequency missense variants in laminin genes LAMA5 and LAMB1 which, together with previously reported LAMC1, form laminin-511 (LM511). AlphaFold 2 protein modeling suggests that mutations at LAMA5 and LAMB1 may destabilize LM511 by altering inter-domain interactions or extracellular matrix binding. Finally, phenome-wide association scans and co-localization analyses suggest that the TCF4 CTG18.1 trinucleotide repeat expansion leads to dysregulation of ion transport in the corneal endothelium and has pleiotropic effects on renal function.

Predictors of Receiving Keratoplasty for Fuchs' Endothelial Corneal Dystrophy among Medicare Beneficiaries

PURPOSE

To identify factors associated with receipt of endothelial keratoplasty (EK) and penetrating keratoplasty (PK) in patients with Fuchs' endothelial corneal dystrophy (FECD).

DESIGN

Retrospective cohort study.

PARTICIPANTS

Medicare beneficiaries 65 years of age or older with a FECD diagnosis between 2011 and 2019.

METHODS

The 100% Medicare fee-for-service administrative claims database was queried for treatment-naïve FECD patients. A multivariate logistic regression model including age, race and ethnicity, sex, geography, ocular comorbidities and surgeries, Charlson comorbidity index (CCI), and socioeconomic status was used to identify factors associated with receipt of EK and PK. Kaplan-Meier survival analyses were used to determine the rate of EK after cataract or complex or other anterior segment surgery.

MAIN OUTCOME MEASURES

Factors associated with receipt of an EK or PK, plus rate of EK after cataract or complex or other anterior segment surgery.

RESULTS

Of 719 066 beneficiaries identified, 31 372 (4.4%) received an EK and 2426 (0.3%) received a PK. In a multivariate analysis, female sex decreased likelihood of both EK and PK (adjusted odds ratio 0.83 [95% confidence interval 0.81-0.85] and 0.84 [0.78-0.92], respectively), while Western residence (1.33 [1.29-1.38]; 1.25 [1.11-1.42]) compared to Southern and history of complex or other anterior segment surgery (1.62 [1.54-1.70]; 5.52 [4.97-6.12]) increased the likelihood of both. Compared to Whites, the likelihood of EK was decreased for Black (0.76 [0.72-0.80]), Asian or Pacific Islander (0.54 [0.48-0.61]), and Hispanic or Latino (0.62 [0.55-0.70]) race and ethnicity, while for the same groups likelihood of PK was increased (for Black 1.32 [1.14-1.53]; Asian/Pacific Islander 1.46 [1.13-1.89]; and Hispanic/Latino 1.62 [1.25-2.11]). Following cataract or complex/other anterior segment surgery, rates of EK were 1.3% and 3.3% at 1 year and 2.3% and 5.6% at 8 years, respectively.

CONCLUSIONS

In a multivariate analysis, women beneficiaries are less likely to receive EK or PK for FECD compared with men, whereas non-White beneficiaries are less likely to receive EK and more likely to receive PK compared with White beneficiaries.

Disease Expression and Familial Transmission of Fuchs Endothelial Corneal Dystrophy With and Without CTG18.1 Expansion

Purpose

To characterize inheritance, penetrance, and trinucleotide repeat expansion stability in Fuchs endothelial corneal dystrophy (FECD).

Methods

One thousand unrelated and related subjects with and without FECD were prospectively recruited. CTG18.1 repeat length (CTG18.1L) was determined via short tandem repeat assay and Southern blotting of leukocyte DNA. Multivariable logistic regression and generalized estimating equation models were employed.

Results

There were 546 unrelated FECD cases (67.6% female; 70 ± 10 years) and 235 controls (63.8% female; 73 ± 8 years; all ≥ 50 years). CTG18.1 expansion (CTG18.1exp+) was observed in 424 (77.7%) cases and 18 (7.7%) controls (P = 2.48 × 10-44). CTG18.1 expansion was associated with FECD severity (P = 5.62 × 10-7). The family arm of the study included 331 members from 112 FECD-affected families; 87 families were CTG18.1exp+. Autosomal dominant inheritance with variable expression of FECD was observed, regardless of expansion status. FECD penetrance of CTG18.1 expansion increased with age, ranging from 44.4% in the youngest (19-46 years) to 86.2% in the oldest (64-91 years) age quartiles. Among 62 parent-offspring transmissions of CTG18.1exp+, 48 (77.4%) had a change in CTG18.1L ≤ 10 repeats, and eight (12.9%) were ≥50 repeats, including five large expansions (∼1000-2000 repeats) that contracted. Among 44 offspring who did not inherit the CTG18.1exp+ allele, eight (18.2%) exhibited FECD.

Conclusions

CTG18.1 expansion was highly associated with FECD but demonstrated incomplete penetrance. CTG18.1L instability occurred in a minority of parent-offspring transmissions, with large expansions exhibiting contraction. The observation of FECD without CTG18.1 expansion among family members in CTG18.1exp+ families highlights the complexity of the relationship between the FECD phenotype and CTG18.1 expansion.

Fuchs endothelial corneal dystrophy: The vicious cycle of Fuchs pathogenesis

Fuchs endothelial corneal dystrophy (FECD) is the most common primary corneal endothelial dystrophy and the leading indication for corneal transplantation worldwide. FECD is characterized by the progressive decline of corneal endothelial cells (CECs) and the formation of extracellular matrix (ECM) excrescences in Descemet's membrane (DM), called guttae, that lead to corneal edema and loss of vision. FECD typically manifests in the fifth decades of life and has a greater incidence in women. FECD is a complex and heterogeneous genetic disease where interaction between genetic and environmental factors results in cellular apoptosis and aberrant ECM deposition. In this review, we will discuss a complex interplay of genetic, epigenetic, and exogenous factors in inciting oxidative stress, auto(mito)phagy, unfolded protein response, and mitochondrial dysfunction during CEC degeneration. Specifically, we explore the factors that influence cellular fate to undergo apoptosis, senescence, and endothelial-to-mesenchymal transition. These findings will highlight the importance of abnormal CEC-DM interactions in triggering the vicious cycle of FECD pathogenesis. We will also review clinical characteristics, diagnostic tools, and current medical and surgical management options for FECD patients. These new paradigms in FECD pathogenesis present an opportunity to develop novel therapeutics for the treatment of FECD.

TCF4-mediated Fuchs endothelial corneal dystrophy: Insights into a common trinucleotide repeat-associated disease

Fuchs endothelial corneal dystrophy (FECD) is a common cause for heritable visual loss in the elderly. Since the first description of an association between FECD and common polymorphisms situated within the transcription factor 4 (TCF4) gene, genetic and molecular studies have implicated an intronic CTG trinucleotide repeat (CTG18.1) expansion as a causal variant in the majority of FECD patients. To date, several non-mutually exclusive mechanisms have been proposed that drive and/or exacerbate the onset of disease. These mechanisms include (i) TCF4 dysregulation; (ii) toxic gain-of-function from TCF4 repeat-containing RNA; (iii) toxic gain-of-function from repeat-associated non-AUG dependent (RAN) translation; and (iv) somatic instability of CTG18.1. However, the relative contribution of these proposed mechanisms in disease pathogenesis is currently unknown. In this review, we summarise research implicating the repeat expansion in disease pathogenesis, define the phenotype-genotype correlations between FECD and CTG18.1 expansion, and provide an update on research tools that are available to study FECD as a trinucleotide repeat expansion disease. Furthermore, ongoing international research efforts to develop novel CTG18.1 expansion-mediated FECD therapeutics are highlighted and we provide a forward-thinking perspective on key unanswered questions that remain in the field.

•

FECD is a common, age-related corneal dystrophy.

•

The majority of cases are associated with expansion of a CTG repeat (CTG18.1).

•

FECD is the most common trinucleotide repeat expansion disease in humans.

•

Evidence supports multiple molecular mechanisms underlying the pathophysiology.

•

Novel CTG18.1-targeted therapeutics are in development.

Association of rs613872 and Trinucleotide Repeat Expansion in the TCF4 Gene of German Patients With Fuchs Endothelial Corneal Dystrophy

PURPOSE

To investigate single nucleotide polymorphisms (SNPs) and trinucleotide repeat (TNR) expansion in the transcription factor 4 (TCF4) gene in a large cohort of German patients with Fuchs endothelial corneal dystrophy (FECD).

METHODS

Genomic DNA was obtained from 398 patients with FECD and from 58 non-FECD controls. Thirty-seven previously reported SNPs were evaluated by genotyping. The 398 FECD samples were analyzed for TNR expansions by short tandem repeat assays and Southern blotting. The possible associations between the TNR length and clinical parameters (age, sex, visual acuity, and central corneal thickness) were analyzed in 132 patients.

RESULTS

The SNPs in COL8A2, TCF8, LOXHD1, and AGBL1 showed no heterogeneity in 36 cases, although SLCA411 showed 3 nonsense mutations. SNPs were detected for TCF4 (rs613872, rs2123392, rs17089887, rs1452787, and rs1348047), but only rs613872 showed a significant association with FECD (P = 9.93 × 10). Overall, 315/398 (79%) patients harbored TNR lengths >50, whereas no non-FECD controls harbored TNR lengths >50. The TCF4 SNP rs613872 genotype was TT: 39 (67%), TG: 18 (31%), and GG: 1 (2%) in non-FECD controls; TT: 39 (47%), TG: 38 (46%), and GG: 6 (7%) in FECD cases harboring TNR <50; and TT: 23 (8%), TG: 224 (79%), and GG: 38 (13%) in FECD cases harboring TNR >50 (P = 2.93 × 10). No significant association was detected between the TNR length and clinical parameters.

CONCLUSIONS

Our large German cohort demonstrated a significant association between the risk allele G in rs613872 and FECD, irrespective of TNR expansion, although this risk allele was more frequent in FECD cases with TNR expansion than without.

The Molecular Basis of Fuchs' Endothelial Corneal Dystrophy

Fuchs' endothelial corneal dystrophy (FECD) is a common disease resulting from corneal endothelial cell dysfunction. It is inherited in an autosomal dominant fashion with incomplete penetrance, and with a female bias. Approximately half of cases occur sporadically, and the remainder are familial. Early and late-onset forms of the disease exist. A review of the literature has revealed more than 15 genes harbouring mutations and/or single nucleotide polymorphisms associated with FECD. The proteins encoded by these genes cover a wide range of endothelial function, including transcription regulation, DNA repair, mitochondrial DNA mutations, targeting of proteins to the cell membrane, deglutamylation of proteins, extracellular matrix secretion, formation of cell-cell and cell-extracellular matrix junctions, water pump, and apoptosis. These genetic variations will form the platform for the further understanding of the pathological basis of the disease, and the development of targeted treatments. This review aims to summarise known genetic variations associated with FECD, discuss any known molecular effects of the variations, how these provide opportunities for targeted therapies, and what therapies are currently in development.